It’s now the 18th of August, a few weeks past the typical date that activity really ramps up across the Atlantic Basin, and there are no named storms to be found. Are all of the forecasts for a very active season going to bust? I don’t think so, and I’ll attempt to explain why. First of all, let’s look at our best analog year for comparing to the current setup across the tropics - 1998. So far, 2010 is progressing very much like 1998 as far as the current La Niña conditions across the Pacific as well as the general atmospheric flow patterns across the Atlantic Basin. In fact, 1998 is nearly a dead ringer for what we’re seeing across the tropics right now.
In 1998, there were 14 named storms, 10 of which were hurricanes. Note that it’s a coincidence that the 2010 list of names is mostly the same list that was used in 1998, twelve years ago. There are 6 years of Atlantic Basin names that rotate each season. The first hurricane of 1998, Category 3 Bonnie with 115 mph winds, did not form until August 19th. It struck the coast of North Carolina late on August 26th. In 2010, the first hurricane of the season, Category 2 Alex, formed in late June. The second hurricane of the 1998 season, Danielle, did not form until August 24th. But after then, the floodgates were opened and the hurricanes kept coming through November. Category 2 Georges struck Mississippi. Category 5 Mitch killed tens of thousands of people in Central America in late October. Hurricane Nicole formed on the 24th of November and lasted until the 2nd of December.
The image above is a snapshot of the activity across the Atlantic Basin on September 26th of 1998. There were actually four hurricanes active at the same time. That date is still over five weeks away, plenty of time for quite a bit of development. And we’re seeing strong signals that the tropics are about to come alive.
As I mentioned in last week’s blog posting, the season typically ramps up quite quickly in early August. That didn’t happen (yet) this August. The reason for the delayed start this August is that there was a burst of dry, stable air that flowed off the west coast of Africa in late July. This resulted in a stabilizing of the atmosphere across the deep tropics. Hurricanes can’t develop in a stable environment. The graphic below clearly illustrates the drop in instability that occurred in late July (blue line). But just in the past few days, instability is rising sharply, up to the “normal” line. I suspect it’s going to rise to above normal levels by next week. The result may be a burst of development over the next few weeks.
For the past week, most of the global computer models have been forecasting the development of between 2 and 4 named storms starting this coming weekend. Below is a one-week forecast from the American “GFS” model. The map is valid Wednesday, August 25th. Note what appears to be a tropical storm forming off the U.S. East Coast early next week and what looks like a strong hurricane impacting the northeast Caribbean. A weaker (developing?) low is indicated east of the Caribbean on this date. And it’s not just the American model forecasting such development. The European and Canadian models are also quite bullish on significant development over the next week or two.
Finally, let’s take a look at the sea surface temperatures across the main development region (MDR) that extends from the eastern Caribbean to near the west coast of Africa. The graphic below indicates that temperatures are at record levels, even higher than 2005 when 28 named storms developed. So there is plenty of heat available for intensification once development occurs. There is so much heat content available that I’d be surprised if we didn’t see at least one Category 5 hurricane develop in the coming months.
The bottom line is that our analog seasons suggested a late start to the real action. And the signals we’re seeing out there across the tropics today indicate that the tropics are about to come alive with development. Will the named storms total the 17 that we predicted earlier this month? Possibly. But with the later start than we expected, that total may be closer to 15 or 16 named storms. Just remember, it’s not how many that form that counts, it’s where they strike that makes all the difference. The steering flow we’re seeing still indicates a high impact threat to the central to northeast Gulf Coast and the southeast U.S. Coast.