Impact Weather: Your Weather Department

Chris Hebert
Chris Hebert,  ImpactWeather’s lead hurricane forecaster
With a B.S. in Meteorology from Texas A&M University and more than 27 years of forecasting experience, Chris is ImpactWeather’s lead hurricane forecaster. For a detailed bio…


It’s Time to Get Ready for an Active 2011 Hurricane Season
April 7th, 2011

The 2011 hurricane season is fast-approaching, as is the 22nd Annual Hurricane Seminar for Business and Industry, scheduled for May 24th at the Houston Hobby Airport Hilton.   Please join us for the most comprehensive and fundamentally educational hurricane seminar yet. Instructional and entertaining, this year’s lineup will provide business and industry leaders with the best information available about what’s important to help you and your company get prepared and stay prepared. The theme of this year’s seminar will be “Innovation, New Techniques and What to Expect in 2011.”  Speakers include some of the top hurricane scientists in the field, including Dr. Phil Klotzbach who will give his (and Dr. Bill Gray’s) outlook for the coming hurricane season.

Speaking of the 2011 outlook, our preliminary 2011 hurricane season outlook, released in February, indicates that the 2011 hurricane season may be a busier one for the Gulf of Mexico and for the U.S. mainland.  Above-normal sea surface temperatures combined with lower-than-normal wind shear will likely result in quite an active season.  Early projections are that the Bermuda High pressure system may be stronger than in 2010.  This could prevent most of the hurricanes from recurving northward well east of the U.S. (as was the case in 2010) and increase the landfall risk to the Caribbean islands and the U.S.  

Recently, we’ve begun production of a series of short videos detailing the Top 10 Problems with Most Hurricane Response Plans.  After working with a number of different companies over the past 5 years, we have developed a list of common problems for you to be aware of.   Not only do we identify the problems, we suggest the solutions.  The problems are presented in the form of a countdown.  Take a look at the videos and see if you can identify some of these problems with your company’s hurricane response plan.

Some 2010 Hurricane Season Oddities
November 17th, 2010

In my last blog entry, I discussed how active the 2010 season was compared to normal.  Fortunately for the U.S., all 12 of this year’s hurricanes missed the United States.  Last week, I thought that we might just see one more named storm before the Atlantic shut down.   Models had been predicting development in the southwest Caribbean to occur a few days ago, but that didn’t happen.  Now it appears that the season may well have ended with the totals of 19 named storms, 12 hurricanes and 5 major hurricanes.

As an interesting final note concerning the 2010 season, Dr. Phil Klotzbach of Colorado State University (works with Dr. Bill Gray) has come up with a number of “oddities” from this year’s hurricane season.  Dr. Klotzbach’s full review of the 2010 season can be found at his website.  By the way, Dr. Klotzbach is scheduled to be our keynote speaker at our 2011 ImpactWeather Hurricane Seminar, tentatively scheduled for Thursday, May 26th.

Here are a few of Dr. Klotzbach’s 2010 oddities:

• Nineteen named storms occurred during 2010. Since 1944, only 1995 (19) and 2005 (28) have had the same or more named storms.

• Nine named storms formed in the Main Development Region this year (Colin, Danielle, Earl, Fiona, Gaston, Igor, Julia, Lisa and Tomas).  Only 1933 (11 storms) and 1995 (9 storms) have had as many named storms form in the Main Development Region.

• 88.25 named storm days occurred in 2010.  This ties 2010 with 2008 for the 6th most named storm days in a single season since 1944.

• Twelve hurricanes occurred in 2010. Since 1944, only two seasons, 1969 (12) and 2005 (15) have had the same or more hurricanes in a single season.

• 37.50 hurricane days occurred in 2010. This is the most hurricane days observed in a single season since 2005 (when 49.75 hurricane days were recorded).

• 5 major hurricanes formed during the 2010 hurricane season. Since 1944, only seven seasons (1950, 1955, 1961, 1964, 1996, 2004, and 2005) have had more than five major hurricanes form.

• 11 major hurricane days occurred in 2010. This is the 11th most major hurricane days to occur in a single season since 1944.

• The season accrued an Accumulated Cyclone Energy  (ACE) of 163. This is the most ACE since 2005 (250) and the 13th most since 1944.

• No Category 5 hurricanes developed in 2010. This is the third consecutive year with no Category 5 hurricanes. The last time that two or more years occurred in a row with no Category 5 hurricanes was 1999-2002.

• June and July had slightly above-average ACE activity. Seven ACE units were accrued during the two-month period, while the 1950-2000 June-July average was approximately 5 ACE units.

• No named storm days were accrued between August 9 and August 21. The last time that no named storm days occurred between these two dates was 2006.

• August had well above-average ACE activity. 38 ACE units were recorded during the month, which is approximately 165% of the 1950-2000 average. It was the most ACE accrued during the month of August since 2005 when 39 ACE units were accumulated.

• Eleven named storms formed between August 22 and September 29. This is the most named storms to form during this period, breaking the old record of nine named storms set in 1933, 1949, 1984 and 2002.

• Five hurricanes formed during the month of October. Only 1870 (six hurricanes) and 1950 (five hurricanes) have had at least five systems reach hurricane strength for the first time during October.

• Hurricane Alex became the most powerful hurricane during the month of June, in terms of maximum sustained winds (85 knots), since Hurricane Alma in 1966 which had estimated maximum sustained winds of 110 knots.

• Hurricane Igor generated 43 ACE units. This is the most ACE units generated by a single storm since Hurricane Ivan (2004) which generated a whopping 70 ACE units.

• Hurricane Julia became the farthest east that a Category 4 hurricane has formed in the Main Development Region, according to the HURDAT database. However, it should be cautioned that the reliability of tropical cyclone statistics, especially in the eastern Atlantic is suspect prior to satellite imagery being readily available in the mid 1960s.

• Igor and Julia both were at Category 4 status on September 15. The only other time that two storms both were at Category 4 status in the Atlantic was on September 15, 1926.

• Igor, Julia and Karl were all at hurricane strength at the same time. This has only occurred in eight years prior to 2010, with the most recent occasion being in 1998.

• Four Category 4 hurricanes (Danielle, Earl, Igor and Julia) formed in the Atlantic between August 27 and September 15 (20 days). This is the shortest time span on record for four Category 4 hurricanes to develop, breaking the old record of 24 days set in 1999.

• Only one tropical storm made U.S. landfall this year (Bonnie). We have not had a hurricane landfall since Hurricane Ike in 2008. The last time that we went two years in a row with no hurricane landfalls was 2000-2001.

• Only three tropical storms have made landfall over the past two years. The last time that three or fewer tropical cyclones made landfall in any consecutive two-year period was 1990-1991.

• No hurricanes made landfall along the Florida Peninsula and East Coast. This marks the fifth year in a row with no hurricane landfalls along this portion of the U.S. coastline. This is the first time since reliable U.S. records began in 1878 that no hurricanes have made landfall along the Florida Peninsula and East Coast in a five-year period.

• No hurricanes made landfall along the United States coastline this year. This is the first time in recorded history that as many as twelve hurricanes have occurred in the Atlantic basin without a United States landfall. Every other year with at least ten hurricanes in the Atlantic basin had at least two hurricane landfalls in the United States.

• No major hurricanes made U.S. landfall this year. Following seven major hurricane landfalls in 2004-2005, the U.S. has not witnessed a major hurricane landfall in the past five seasons. The five consecutive years between 1901-1905 and 1910-1914 have been the only other five consecutive year periods with no major U.S. hurricane landfalls.

That’s some list for this year!  So much activity and so little U.S. impact in 2010.  That’s something those of us in the U.S. can be thankful for.

2010 - the Most Active “Inactive” Season on Record
November 9th, 2010

For residents of the U.S., the 2010 hurricane season will be remembered for how quiet it was.  Had it not been for the very weak Tropical Storm Bonnie which struck south Florida or the quite strong Tropical Storm Hermine that crossed the Mexican border into deep South Texas, the U.S. would have made it through the 2010 season unscathed.   Little would U.S. residents know that the pre-season predictions of a “hyperactive” 2010 hurricane season with 17-20 named storms had actually come true!

                                 2010 Numbers vs. a 1950-2009 Seasonal Average

In fact, the 2010 season ranks as one of the most active seasons on record, with 19 named storms, 12 hurricanes and 5 major hurricanes.  Only 1933 and 2005 had more named storms, and only 2005 had more hurricanes (15) than we saw this year in the Atlantic Basin.  Accumulated Cyclone Energy (ACE), a measure of seasonal activity that takes into consideration how strong the season’s storms were and how long they lasted, was in the “hyperactive” range, with a total of 159.5 ACE points.  A seasonal ACE of 103 is about normal, 150 is considered to be hyperactive. Below are a few of the statistical highlights of the 2010 season:

  • Alex – Second strongest June hurricane on record
  • Aug. 22-Sep. 29 – a record 11 named storms
  • Most active season on record with no U.S. land falling hurricane
  • Hurricane Karl – strongest hurricane to ever hit Veracruz, MX.  Also, the only major hurricane ever recorded in the southern Bay of Campeche
  • 12 hurricanes and no U.S. hit – never happened before. Historically, 1 in 4 Atlantic hurricanes hits the U.S.

The 2010 season was a record-breaking one numbers-wise and nobody got hit?  Not quite.  Even though the U.S. wasn’t hit by a hurricane this season, other areas were not so fortunate.  Mexico suffered through 10 landfalls, including 3 hurricane landfalls, one of them a major hurricane (Karl). The northeast Caribbean was grazed by major Hurricane Earl and experienced some of the heaviest rainfall every recorded from Tropical Storm Otto that passed well to the north of the Caribbean.  Nova Scotia was slammed by Hurricane Earl, and Newfoundland was hit by one of the worst hurricanes in its history, Igor.  Igor’s heavy rain and strong wind wiped out large sections of the Trans-Canada highway in northeastern Newfoundland.  Belize experienced 4 landfalls, including Hurricane Richard.


The graphic above indicates the regions that we had predicted might be more at risk for a hurricane landfall in 2010.  I’ve added in all the landfalls on the map.   We really thought that the pattern setting up last spring indicated a high risk of a land falling hurricane across the southeast U.S. (Florida).  Fortunately for the U.S., the area of low pressure that we expected to be near the East U.S. Coast actually positioned itself just offshore, keeping a number of major hurricanes east of the U.S.

2010 Season Tracks (courtesy Unisys:  http://weather.unisys.com/hurricane/)

It’s hard enough to predict seasonal activity, and it’s even harder to predict where a hurricane might make landfall 3-6 months before it forms.  Just be thankful (U.S. residents) that the area of low pressure positioned itself just a little closer to the East U.S. Coast than had been predicted back in May. Had it not been for that, the U.S. may well have been hit by several major hurricanes this season.    As I’ve always said, and “active” season is one in which you are directly hit by a storm.  I’m thankful for the “inactive” season here in the U.S.

After such a season as this, what might the 2011 season have in store for us?  Early indicators are that La Niña will be fading by next summer, but  there will be no El Niño in its place. Instead, look for a weak La Niña to Neutral conditions in 2011.  Such conditions would indicate another active hurricane season, perhaps with 15 named storms. I don’t think the U.S. can count on being so lucky as to escape any hurricane landfalls in 2011.

Another Hurricane in the Caribbean Next Week?
October 26th, 2010

 In our 2010 season outlook, we stated that a moderate to strong La Niña would likely result in storms developing through October and right through the month of November.  So far in October, we’ve seen hurricanes Otto, Paula and Richard form. That’s one per week..  Currently, there’s a storm center located about 1500 miles east-northeast of the Caribbean with winds to tropical storm strength.  The National Hurricane Center has identified the storm as “Invest 90L”.  We’ve identified it as the Tropical Disturbance 66.  It’s a storm center with 40 mph winds, so the NHC could name it at any time this week.  But this isn’t the storm I’m concerned about.  It’s our  Disturbance 67 in the central Tropical Atlantic  that could develop in the Caribbean next week.

TropicsWatch Daily Briefing Map for Tuesday, October 26th

As of Tuesday morning, Disturbance 67 was located about midway between the eastern Caribbean and the west coast of Africa between about 3N-10N latitude.  It’s a strong tropical wave that has some mid-level rotation associated with it.  Atmospheric conditions are not favorable for any development now, but the disturbance will be reaching the eastern Caribbean early next week where conditions may allow for some slow development. In fact, the American, European and Canadian computer models have been predicting this disturbance to develop in each model run over the past 2-3 days.  With such model agreement on development, we do need to pay attention to this disturbance.  Let’s take a look at what the models are forecasting.

American Model (GFS) Forecast Valid Next Wednesday, November 3rd

The American Model has been consistent in forecasting a rather sharp East U.S. Coast trough and an associated cold front extending into the western Caribbean by next Wednesday/Thursday.  South and southwesterly winds aloft ahead of the cold front would pick up any developing storm over the central Caribbean and carry it northward, possibly toward Jamaica or the Dominican Republic/Haiti.   Such a track would not be too uncommon for early November.  High pressure building over the Gulf of Mexico would prevent any movement in that direction.  The European model has a different solution, however.

European Model (ECMWF) Forecast Valid Next Thursday, November 4th

Though the European model develops a storm in the south-central Caribbean on Wednesday, similar to the American model, it indicates a much weaker trough and associated cold front off the East U.S. Coast next week.  The combination of a weaker front and weaker storm system could leave the storm trapped in the southwest Caribbean for a while, embedded within relatively light steering currents.  This solution, too, is fairly common in November.  At least both models are in general agreement that any storm developing in the Caribbean next week will probably not become a threat to the Gulf of Mexico, probably being the key word there.    If the European model prediction verifies, and the storm becomes stationary in the southwest Caribbean next week, then it’s not a 100% certainty that it couldn’t be steered toward the Yucatan Channel late next week. In that case, it could possibly become a threat to south Florida.  Chances of that appear to be low, though.

So here we are with 17 named storms, 10 hurricanes and 5 major hurricanes as we near the last month of the 2010 hurricane season.   Our June 1st forecast was for 18 named storms, 11 hurricanes and 5 major hurricanes.  With one more Caribbean hurricane next week, we’d precisely hit our seasonal forecast, numbers-wise.    But I’m not so sure there won’t be another storm or two during the month of November.

Will Tropical Storm Richard Threaten the Northern Gulf of Mexico?
October 22nd, 2010

The seventeenth named storm of the 2010 hurricane season is now churning around in the western Caribbean Sea.  Tropical Storm Richard is located about 150 miles east of Honduras with 40 mph winds.  Satellite imagery indicates that Richard is becoming better organized today, as wind shear has decreased significantly during the past 24 hours.  Question is, will Richard pose a serious threat to either the Bay of Campeche or the northern Gulf of Mexico?

It did look like Richard might have a chance to impact the northeast Gulf yesterday, but those chances are decreasing.  High pressure is building across the northwest Gulf a little more strongly than had been forecast.  This should keep Richard on a west to west-northwesterly track up until its landfall in Belize on Monday.  With a favorable environment for intensification over the next 60-72 hours, Richard will quite likely reach hurricane strength by Sunday, and possibly even major hurricane strength of 115 mph winds before it moves inland.  That is, if it stays to the north of the coast of Honduras, which is no by no means a certainty.

Where will Richard go beyond the next few days?  Before I answer that, let’s have a look at some past storm climatology.  It’s always interesting to see where past storms that were located in the same area eventually tracked.  In the image below, I plotted all storms since 1851 that moved to within 85 miles of Richard’s current position during the months of October and November.

1851-2009 October/November Storms Passing Within 85 Miles of Richard’s Current Location

Note that the vast majority of October/November storms in the western Caribbean Sea tracked northward toward Cuba and eventually Florida and/or the Bahamas. But that won’t likely be the case with Richard, as high pressure is forecast to build over Florida by next week, keeping Richard away from the state.  Earlier this week, we thought that Richard might track toward the Florida Panhandle by next Thursday.  Note on the image above that the last time a storm took such a track from Richard’s current position was in 1916.  So it doesn’t happen often.  And Texas has never been hit from a storm in Richard’s current location.   So much for climatology, let’s take a look at where the latest computer models say that Richard might go.

Computer Model Forecasts for Richard as of 7AM CDT October 22

It seems that all of the models are in much better agreement today.  They all now see that the high pressure center over the northern Gulf over the next 3-5 days will be stronger than was previously forecast.  That should keep Richard farther to the south, preventing any turn toward the southern Gulf over the next 2-3 days.   I think that after Richard moves inland into Central America on Monday morning, it may well survive to reach the eastern Bay of Campeche late next Tuesday.  Once in the Bay of Campeche, though, it may not be able to survive for too long.

The reason for that is a moderate cold front that is forecast to push off the Texas coast late Wednesday and reach the southwest Gulf and Bay of Campeche on Thursday.  What’s left of Richard will most likely entrain cooler, drier air and merge with the frontal boundary rather than intensify and head off to the north or northeast.

Will Richard be the final storm of the 2010 season? Probably not.  There are still five weeks to go in the season, and some of the long range models are already hinting at another storm developing in the eastern Caribbean Sea by late next week.  When all is said and done, the 2010 season may end with 18 or 19 named storms, making it one of the five most active on record, and the most active on record without a U.S. hurricane landfall.

Major Hurricane in the Caribbean Next Week?
October 15th, 2010

All the main global models have come on board forecasting the development of the 17th storm of the 2010 hurricane season in the southwest Caribbean next week.  The southwest Caribbean is the place where late-season development typically occurs, so this is something to be expected, particularly during a strong La Nina season.  Our best 2010 analog season, 1998, featured Category 5 Hurricane Mitch developing in the southwest Caribbean on the 22nd of October.  Mitch killed over 20,000 people in Central America and southern Mexico.  And in 2005, another analog for 2010, Hurricane Wilma, the strongest hurricane in Atlantic Basin history, formed in the southwest Caribbean on October 15th.

With such model support for development, I think we may well see a storm develop to the east of Nicaragua around next Tuesday, October 19th.  Question is, where will it go?  I can tell you where it isn’t likely to go - the northwest or north-central Gulf of Mexico.  Persistent and rather strong mid and upper-level westerly wind flow across the central to northern Gulf of Mexico would steer any tropical cyclone moving out of the northwest Caribbean Sea almost immediately to the northeast toward south Florida or the Bahamas.   And that may well be the fate of this potential storm.

Long-range models predict a rather deep trof and associated cold front across the eastern U.S. toward the end of next week.  Such a feature would mean that steering currents could pick up anything developing in the western Caribbean and carry it northwest toward central to western Cuba by next Friday or Saturday.  With the trof/front in place across the southeastern U.S., the storm could track to the north-northeast or northeast, possibly threatening southern Florida and/or the Bahamas before racing northward and out to sea.  I think that this might be the most likely track of the storm should it develop.  But there is another possibility - it could be blocked by high pressure building in behind the cold front to the north and shoved westward into Central America and/or southern Mexico, as was Hurricane Mitch in 1998.

As for its potential intensity, conditions aloft look quite favorable for strengthening next week.  And with oceanic heat content quite high across the western and northwest Caribbean, any storm developing in the region next week could easily become a major Category 3 or 4 hurricane.  I’d say possibly a Category 5, but I’m a bit wary of the fact that conditions across the region have been a little unfriendly toward development for some reason that we don’t understand this season.

Residents of the western Caribbean islands, South Florida and the Bahamas should pay close attention to the tropics over the coming days, as your season is not likely over just yet.

Paula - The 9th Hurricane of the 2010 Season
October 12th, 2010

The 2010 hurricane season is well on its way to being classified as “hyperactive”, though you wouldn’t know it if you live along the U.S. Coast.  With Hurricane Paula forming in the northwest Caribbean last night, that makes 16 named storms, 9 hurricanes and 5 of those hurricanes major hurricanes.   This would make the 2010 season one of the most active on record, and probably the most active season without a hurricane landfall along the U.S. Coast.  Fortunately for the U.S., all the hurricanes this year have tracked either into Mexico, Bermuda, eastern Canada, or safely out to sea.  And it looks like Paula will not be an exception.

Although hurricanes which form in the northwest Caribbean in October and November frequently impact the southern Florida Peninsula (think Wilma in late October of 2005), the jet stream will be unusually far to the south across the Gulf of Mexico (and Florida) over the next week or two.   This means that should Paula approach western Cuba, then it could be steered sharply to the east-northeast toward the Bahamas while experiencing increasing wind shear.  The increasing wind shear should result in steady weakening.  Though it is possible that the Florida Keys could experience tropical storm conditions in a worst-case scenario, hurricane conditions are unlikely there.

Across the central and northern Gulf of Mexico, the jet stream is blowing quite strongly from west to east, protecting that region from any storms.  And it looks like the protection will continue through the month of October.   I don’t see any signs of the upper-level winds diminishing across the Gulf over the next few weeks.   Though the hurricane season may be effectively over for the northern Gulf lease areas and the Gulf Coast, it’s still not over for Florida.  Some models indicate another hurricane developing in the western Caribbean next week, so Florida may  not be out of the woods just yet.  Given the strong La Nina present in the Tropical Pacific, we may see additional development in the western Caribbean well into November this year.

When all is said and done, the 2010 hurricane season may end with as many as 17-20 named storms, which is quite close to the pre-season forecasts.  But the season will probably end without a U.S. hurricane landfall.

Hurricane Threat for the Gulf of Mexico Next Week
September 21st, 2010

For the past few weeks, I’ve been discussing an upcoming pattern shift that would lead to tropical cyclone development in the Caribbean Sea between the 20th and 30th of September vs. the far eastern Atlantic (Danielle, Earl, Fiona, Gaston, Igor, Julia and Lisa). Long-range models were quite supportive of this idea from early in September. As of today, it looks like those long-range models are going to be right.

We’ve been following a tropical wave across the Atlantic for the past week. This wave, which we have identified as Tropical Disturbance 51, is now located in the eastern Caribbean Sea. On a side note, this wave appears to be the same one which spawned Hurricane Igor last week. Sometimes tropical waves can spawn several storms. Tropical Disturbance 51 appears to be getting better organized by the hour. A reconnaissance plane is scheduled to investigate it on Wednesday. I’m not sure if it will be strong enough to get upgraded to a tropical depression by then, but I think it may well be a depression or even a tropical storm by Thursday afternoon.

Although there was considerable disagreement among the various global models (U.S, Canadian and European) over the weekend as far as the potential track of the system, these models are coming into better agreement today. Such model agreement gives a forecaster more confidence in his or her forecast, but model agreement does not mean that the models are correct. In this case, the models indicate a general west to west-northwest track, taking the center near eastern Honduras on Saturday then northwestward toward the eastern Yucatan Peninsula on Sunday. That’s where the major uncertainty begins.

All of today’s runs bring the center near the eastern Yucatan Peninsula north of Belize on Sunday then move it very slowly northward for the next 2-3 days. By Wednesday, a cold front moving southward across the northern Gulf could pick up the storm and take it northeastward, possibly toward the Florida Peninsula, though the American model takes it across Cuba and south of the Florida Peninsula.

Where will it really go? That’s something I’m not at all sure of - yet. Any time steering currents get so weak such that a storm stalls makes for a very difficult forecast. The forecast track and setup sort of reminds me of Wilma in 2005. Wilma formed in the south-central Caribbean and tracked toward the northeast Yucatan Peninsula where it stalled for several days before being picked up by an approaching front and accelerating off to the northeast across south Florida. But the forecast also reminds me of another quite major hurricane from 1998 - Hurricane Mitch.

Initially, Mitch was forecast to get picked up by an approaching front and track northward into the Gulf. However, the front turned out being too weak and Mitch tracked westward into Nicaragua where it killed 10,000-20,000 people due to torrential rains. For now, my vote would be for the Wilma scenario, with a possible threat to Florida toward the middle to end of next week. That’s a long way out, though, to have much confidence.

One thing that does appear to be likely is that any storm moving into the northwest Caribbean will encounter extremely high oceanic heat content. The northwestern Caribbean Sea is dominated by a pocket of very warm water that is also quite deep. There is plenty enough energy there to support a Category 5 hurricane, not that any of the models is currently forecasting such intensity. But if the storm develops and stays over water, I think that there is certainly the potential that it could become a large and quite powerful Category 4-5 hurricane in the northwest Caribbean this weekend or early next week.

Beyond next week, I’m seeing signals which indicate additional development across the Caribbean Sea as we move into October. I don’t think that the 2010 hurricane season is going to be winding down until late October or November.

We Found All the Hurricanes!
September 14th, 2010

Many people have been asking for the first half of the 2010 season “where are all the hurricanes?”   Well, I think we’ve found them.  Since August 21st, 8 named storms have formed, including three Category 4 hurricanes and Category 2 Julia (Julia reached Category 2 strength at 8PM CDT this evening and could reach Category 3-4 strength tomorrow).  As of this afternoon, we have newly-formed Tropical Storm Karl in the western Caribbean, which I think is destined to become Hurricane Karl in the Bay of Campeche on Friday.  The last 30 days have been extremely active across the tropics, one of the busiest 30-day periods on record.  So far, though, all the big hurricanes have mostly stayed out to sea (Earl reached eastern Canada possibly as a Category 1 hurricane).   But there are signs in the long-range models that the development region may be shifting westward toward the Caribbean Sea and the Gulf of Mexico in the coming weeks.

For the past 3-4 weeks, the Caribbean Sea and Gulf of Mexico region has been dominated by high pressure and sinking air.  The massive ridge over the southern U.S. has kept the region free of any significant storms up until now, but that high pressure area won’t be around forever.   Summer comes to an end next week, and the transition to fall is just the thing that could make the western Atlantic Basin come alive with development.    One long-range signal, the Madden-Julian Oscillation (MJO) is predicting that an upward motion pulse will reach the western Atlantic Basin in the next week or so.

The MJO is a pulse of increasing upward motion and tropical cyclone development that starts in the Indian ocean and travels eastward across Asia, the Pacific and eventually to the western Atlantic Basin.  Wherever this MJO pulse travels, we typically see an increase in tropical cyclone development.  Once it reaches the East Pacific, there is often a significant increase in development across the Gulf of Mexico and the Caribbean Sea.   Just such an MJO pulse is now forecast to reach the East Pacific later this week.   It’s not a strong MJO, but it could significantly increase thunderstorm activity across the Gulf and Caribbean, leading to the development of several storms in the region.

In addition, some of the longer range computer models have been forecasting the development of a hurricane in the central to western Caribbean Sea between about the 21st and 25th of the month (next week).   For 3-4 days now, each run of the American GFS model has forecast such development.  Even the European model is hinting at this development now.  The models are forecasting the high pressure area across the Gulf to break down next week, leading to development in the Caribbean.    I think that there is a very good chance that the models are correct in forecasting such development.

So while the 2010 season has just passed the half way point, it’s looking like the last half of the season will likely bring several hurricane threats to the Caribbean Sea and to the U.S. Gulf Coast, and quite possibly to the southeast U.S. as well.   The strong La Niña out in the Pacific could keep the 2010 season going through October and well into November.  Don’t look for a rapid shut down of the tropics in late September this year.  The worst of the season may be yet to come as far as landfalling hurricanes.

Tropical Storm Igor Forms in East Atlantic
September 8th, 2010

The Cape Verde season just won’t quit after starting late in August.  As a matter of fact, we’ve seen 6 named storms form since August 21st, two of them major hurricanes (Danielle/Earl), and 5 of them forming in the far eastern Atlantic.  Now we have Tropical Storm Igor out there about 2500 miles east of the Caribbean Sea.  Igor’s winds are only 40 mph right now, but I think that Igor is quite likely going to become a large and powerful hurricane in 4-6 days.  The big question is - where will Igor go?

Climatology is often a very good tool for estimating what might or might not happen.  Let’s take a look at all September storms that passed within about 75 miles of Igor’s current position during the month of September and see where the past storms went.  The records start way back in 1851, though not many storms were identified so far east during the 19th Century.  To do this, I like to use the Coastal Services Center’s Hurricane Viewer tool.  When I plugged in the coordinates for Igor (13.7N / -23.5W), selected all storms within 65nm of Igor and then only the month of September, I got the map below:

Pasts Storms Near Igor

What you see on the map above are the tracks of 13 named storms that formed or passed within 75 miles of Igor’s location from 1851-2009 during the month of September only.   Personally, I was shocked when I saw the results of my quick study.   I had expected about 95-100% of storms in the region to recurve east of the Caribbean and head safely out to sea.  But what climatology indicates is that 5 of the 13 storms struck the U.S., and these were big name storms.   Of those 5 that struck the U.S., 2 struck the northeast Caribbean as major hurricanes.  And to top it off, 4 of those 5 hurricanes became Category 5 hurricanes on the Saffir-Simpson Hurricane Wind Scale.  Let’s break those five down:


  • The 1928 Okeechobee Hurricane - Formed on September 6th just east of Igor and tracked just north of west until it entered the northeast Caribbean on  September 12th as a Category 4 hurricane with 135 mph winds. On the evening of September 13th, it became the only Category 5 hurricane (160 mph winds)  in recorded history to make a direct hit on the island of Puerto Rico, killing over 300 people. But it wasn’t done yet, From Puerto Rico it tracked west-northwest straight to southeast Florida where it struck as a Category 4 hurricane with 155 mph winds on the night of the 17th of September.   Over 2500 people died in southeast Florida, many when the dike around Lake Okeechobee broke, flooding an area covering hundreds of square miles.
  • The Great 1938 New England Hurricane - Formed just east of Igor’s current location on September 10th. It tracked to the west-northwest for 9 days, reaching just north of the eastern Bahamas as a Category5 hurricane with 160 mph winds.  So far, no land areas were threatened.  But that’s when the hurricane made a rather sharp turn to the north and accelerated to a speed of nearly 60 mph off the East U.S. Coast.  It struck Long Island early on the 22nd of September as a large and powerful hurricane.  Some records state that it had become extratropical before reaching New England, other records have it as a large Category 3 hurricane at landfall.   But it was the costliest and deadliest hurricane in New England history, killing between 700-800 people and causing property losses of around $306 million dollars ($4.72 billion in 2010 dollars).
  • Fort Lauderdale Hurricane of 1947 - Formed a little east of Igor’s current location on September 4th.  It passed northeast of the islands of the eastern Caribbean on the 13th as a Category 4 hurricane with 135 mph winds.  By the 16th, it had reached Category 5 strength just east of the lower Florida peninsula.  It struck near Fort Lauderdale, FL as a Category 4 hurricane with 155 mph winds on the morning of September 17th, killing 51 people there.  Two days later, it struck southeast Louisiana as a Category 2 hurricane with winds of near 100 mph, producing wind gusts to 110 mph in New Orleans and 120 mph in Baton Rouge.  The hurricane killed 12 people in Louisiana and 22 in Mississippi.
  • Gloria of 1985 - Formed on September 16th very near where Igor is currently located.  It tracked to the west to west-northwest, passing just north of the islands of the eastern Caribbean on the 23rd as a rapidly-intensifying Category 1 hurricane.  By the 25th, Gloria was a strong Category 4 hurricane with 150 mph winds as it passed just northeast of the Bahamas.  Gloria took a turn to the north and grazed the Outer Banks of North Carolina on the evening of the 26th with 105 mph winds then slammed into Long Island with 100 mph winds on the 27th, killing 8 people.
  • Hugo of 1989 -Formed just east of Igor on the 10th of September, tracking westward while slowly intensifying.  Hugo reached Category 5 strength with winds of 160 mph on the 16th, a day before it raked the islands of the northeast Caribbean as a 145 mph Category 4 hurricane.   On the 22nd, Hugo struck South Carolina as a Category 4 hurricane with winds of 145 mph, causing extensive devastation across the Carolinas.

Well that’s quite a list of Caribbean and U.S. impacts from previous hurricanes which have formed or passed near Igor’s current position!  But where will Igor track?  It’s too soon to tell for sure.  Model guidance suggests that Igor will track to the north of the eastern Caribbean in 7-8 days. Thereafter, the models diverge.  Some take Igor off to the north and out to sea, but the European model indicates that Igor’s northward motion could be blocked by high pressure to the north, sending it westward toward the U.S. East Coast.  I think that Igor will most likely take a path safely out to sea, but given the climatology of past storms I’m not 100% confident Igor won’t strike land.