Why did Hurricane Ike get so large?

Well, it's now day four of my promised 7-10 day lull in Atlantic hurricane activity. That prediction still looks reasonable. Heavy thunderstorm activity has begun to increase over the Lesser Antilles Islands, where a tropical wave is interacting with an upper-level low pressure system. This tropical wave is moving westwards at about 15 mph, and has an impressive surge of moisture with it, as seen on animations of total precipitable water from the University of Wisconsin CIMSS group. The region is under about 10-20 knots of wind shear, and probably won't be able to organize much today or Friday due to the shear and presence of the upper-level low pressure system. By Saturday, wind shear is expected to drop over the entire Caribbean, and the upper level wind flow becomes more anticyclonic. These are favorable conditions for tropical cyclone development, and we may have something develop by Sunday in the central or western Caribbean. The NOGAPS is the only major model predicting something will develop. However, most of the models are forecasting the development of a tropical depression off the coast of Africa early next week. I expect we will have Tropical Storm Kyle, either in the Caribbean or off the coast of Africa, by the middle of next week.


Figure 1. Hurricane Ike at 12:05 pm CDT September 12, 2008, as seen by NASA's Terra satellite. Image creidt: NASA Earth Observatory.

Why did Ike get so large?
Hurricane Ike grew unusually large, eventually filling up the entire Gulf of Mexico and becoming larger than Katrina. How did it get so big? Well, one theory is that the storm's passage over Cuba helped it to grow in size. During the day and half the eye of Ike traversed Cuba, the thunderstorm activity near the center was suppressed by land. However, a large portion of the storm was over the exceptionally warm waters of the Loop Current on either side of Cuba. Since the storm couldn't put any energy into intensifying and maintaining its core, the energy pulled out of the Loop Current went into expanding and intensifying the outer portions of the storm that were over water. When Ike finally emerged into the Gulf of Mexico, its scale had been reset to this new larger size, and the storm was able to maintain the new scale. A similar transition to a new larger scale also occurred to Hurricanes Katrina and Andrew after they passed over South Florida.

How you can help
The group of wunderground members that are spearheading their own Hurricane Ike relief effort, aimed at providing assistance and supplies to people that are not in the mainstream relief areas, have now raised $7700. The first relief truck with supplies is on the way to Texas. Deductions are tax-deductible, and can be made in several ways:

Patrap's wunderblog
www.stormjunkie.com
www.portlight.org

Of course, contributing to the Red Cross or your local church is another great way to help out. Thanks!

Jeff Masters