Blasts of warm air from Franklin and the importance of Gert

Gert is gone. A seemingly inconsequential minimal tropical storm, Gert may well turn out to be very important. The reason? The NOAA P-3 aircraft and Gulfstream IV jet did a series of intensive research missions on Gert before, during, and after its formation. They captured a unique data set that may shed light on the little-understood process of how a tropical wave becomes a tropical depression. The NOAA aircraft were also in the storm when it did one of those impossible to forecast "reorganizations", where the center jumped 60 miles in the space of a few hours to center itself under a developing area of intense convection. Forecast models now do a reasonable job predicting the track of tropical cyclones, but are lousy at predicting when they will form and when a storm will undergo a major reorganization. NOAA has been investing in more research to try to improve these models, and hopefully the missions into Gert will help.

Franklin continues to head out to sea and struggle against the strong shear trying to rip it apart. Franklin is only a threat to shipping--unless you believe this news item that went out on the news wire yesterday:

Storm to bring high heat to Florida

Miami - Tropical Storm Franklin strengthened as it spun away from the Bahamas on Saturday and moved farther east in the Atlantic, but blasts of warm air from its core were expected to bring extreme heat the Florida peninsula.

This news story was guilty of presenting some incorrect meteorology. True, Tropical Storm Franklin has a warm core, like all hurricanes and tropical storms do. If the center of Franklin moved directly overhead, one might feel a bit of extra heat (which would be the least of your concerns!) However, "blasts of warm air" certainly are not emanatng from the center of Franklin. The warm core stays pretty shielded from the surrounding environment of a tropical cyclone. Since the winds of these storms spiral into the center, there is really no opportunity for the warm air at the core to emanate out in a "warm blast". If a "warm blast" did emanate from the core, the storm would quickly fall apart! What the article should have said is that the counter-clockwise circulation around Franklin is drawing up hot, humid tropical air into Florida.

Looking out over the rest of the tropics, the only item of note is a large, well-organized wave that just moved off the coast of Africa. The GFS model has this wave turning into a tropical storm in a few days and recurving to the northeast in the middle of the Atlantic Ocean. I'll talk more about this wave tomorrow if it still looks impressive. However, the sea surface temperatures in this region are about 26 - 28C, and 27C is considered the minimum needed for tropical storm formation.

Jeff Masters