As I ended my post last week, Hurricane Ike was churning in the central Gulf and taking a bead on Houston. We had noticed a slight northwesterly jog and were hopeful that this was a sign of an early turn to the north which would spare the Houston-Galveston area. It wasn’t. I was on the rideout team at our office last Friday night, along with about a dozen other brave coworkers. Being meteorologists, we find hurricanes and other storms quite fascinating. That’s why we became meteorologists in the first place. Getting to experience a hurricane first-hand is something most of use would like to do at one point – just not one that’s heading right for our homes and families. We figured that our building was built well enough to handle even a Category 3 hurricane, so we were mostly worried about how our homes would handle the wind and falling trees.
Ike struck Cuba as a powerful Category 4 hurricane but emerged into the Gulf a much weaker Category 1 hurricane with hurricane force winds covering only a few square miles. Crossing a large land mass like Cuba can significantly change a hurricane’s structure. Prior to reaching Cuba, Ike was a relatively small but intense hurricane. Crossing Cuba disrupted Ike’s core significantly. But that’s both good and bad. The good part is that Ike never could get its core regenerated before slamming into Texas last Friday night. This kept Ike from becoming a much more dangerous Category 3 or 4 hurricane. The bad part is that all of Ike’s energy had to go somewhere once its core was disrupted. So instead of strengthening, Ike became a much larger hurricane. Same amount of energy as before, but that energy was spread out over a much larger area. This reduces potential structural damage due to winds, but it significantly increases the size and expanse of the storm surge.
Contrary to popular belief, the height of a hurricane’s storm surge has virtually nothing to do with its Saffir-Simpson rating. In fact, nowhere in the calculation of storm surge is a hurricane’s peak wind speed (its Saffir-Simpson rating) even considered. Those tables that assign a particular storm surge range to a Saffir-Simpson category are worthless and should never be used to estimate storm surge. Yes, a Category 3 hurricane could produce a 9-12 foot surge under certain conditions, but a Category 3 hurricane could also produce a 3 foot surge or a 30 foot surge. What’s more significant is the size of a hurricane’s wind field and the coastal topography in the hurricane’s path. And, as I mentioned above, Ike became a very large hurricane after crossing Cuba. Not intense, but large. I will go into more detail about storm surge in a future post.
Two days from landfall (36 hours from impact of tropical storm conditions), I watched in amazement as local officials in Galveston pondered the need for evacuation. Ike was projected to hit the southwest end of Galveston as a Category 3 hurricane. If that’s not enough to trigger evacuations, then what is? But Ike was “only a Category 2 hurricane” at the time. Many people say they’ll ride out a Category 1 or 2 hurricane, but not a major Category 3 hurricane or greater. These people are uninformed as to the power of even Category 1 hurricane winds and potential storm surge, and they have no idea how quickly a hurricane can strengthen in the hours just prior to landfall. Ike struck the Houston-Galveston area as a Category 2 hurricane. Not a major hurricane, so no big deal, right? Tell that to the residents of the Texas coast whose homes (and lives) were washed away by Ike’s 15-20 foot storm surge.
Yes, Ike was only a Category 2 hurricane at landfall. Friends and neighbors of mine find it hard to believe that a Category 2 hurricane could do so much damage. Ike was actually beginning to intensify as it reached the Texas coast – not enough to become a Category 3 hurricane, but enough to develop a band of hurricane-force winds in its western eyewall. I spent about 6 hours in Ike’s western eyewall Friday night, along with much of Houston. For the most part, most of central and eastern Houston saw strong tropical storm force winds over those 6 hours, but there were a few periods when the wind probably just barely reached sustained hurricane force winds of between 75-80 mph. But that’s probably the strongest wind the Greater Houston area has seen in 50 years, and the trees took quite a beating.
The graphic below is from the Hurricane Research Division (HRD) web site. The contours represent Ike’s wind field at landfall (in knots). I circled Ike’s Category 2 winds in yellow and the Category 1 winds in white. As you can see in the graphic below, valid 2:30AM CDT Saturday, Sept. 13th, Ike’s Category 2 winds were confined to the beach areas near High Island – east of Galveston. The Houston area experienced strong tropical storm force winds and some brief Category 1 winds.
Normally, a hurricane weakens immediately upon landfall. But Ike was different, at least as far as its southwest quadrant of squalls. As Ike moved northward through Houston, its winds actually increased west and southwest of the center. By 8:30AM CDT, Ike’s southwest quadrant had winds of 70 kts (80 mph) as seen in the image below.
So, as Ike was passing east of Houston, its winds on the western side were increasing between 2:30AM CDT and 8:30AM CDT. That means those of us in the fourth largest city in America saw periods of hurricane-force winds for probably the first times in our lives last Friday night. Spending those 6+ hours in Ike’s western eyewall was more than enough excitement for me. I’ve had neighbors come up and ask me about Ike. They can’t believe that the winds which ripped their trees out of the ground and deposited them on their roofs were only lower-end Category 1 winds. Well, that’s a hurricane, folks. There’s no such thing as a minimal hurricane.
It turns out that the European model didn’t do too badly with Ike. It was only off by a few hundred miles on its 7-day forecast. Not bad at all, unless it just happened to track right over your head. I’ve been without power for a week now at my home in southwest Houston. As the temperature climbed yesterday, I went to Lowe’s and purchased a small window AC unit. It’s held in with scrap wood and duct tape, but it works. Let me give you a little advice about purchasing a home generator. Make sure you get one that has a 6-7 gallon tank and runs all night. I actually won mine as a door prize at a local hurricane conference 3 years ago. Worked fine, but the 1 gallon tank runs out of gas every 2-3 hours. Next year I’ll have a new generator, I guarantee you that. But at least it kept the fridge cold (and my neighbor’s fridge).
One final note. There has been a lot of talk about replacing the Saffir-Simpson Hurricane Scale after Category 2 Ike devastated southeast Texas. People are saying that we need a new scale, one that takes into account not only a hurricane’s peak winds but also its size. We developed just such a scale three years ago after the 2005 hurricane season. It’s called the Hurricane Severity Index. Next week, I’ll introduce you to this new scale we’ve developed and we’ll take a look at how Ike rated on the scale compared to some well known hurricanes of the past.
September 25th, 2008 at 11:17 am
I think this is great. You need to remind readers who have generators to check with their local utilities about where and how to hook them up. If improperly connected, they can pose life threatening hazards to the crews that are trying to restore power.