Wilma's formation marks busiest hurricane season ever

The historic Hurricane Season of 2005 now has the distinction of being the busiest ever. Wilma's formation this morning gives 2005 21 named storms, equaling the mark set in 1933. With over six weeks still left in hurricane season, that mark will likely be surpassed.

After struggling for two days as a tropical depression, Wilma finally put together a sustained, intense burst of deep convection this morning that propelled her to tropical storm strength. This convective burst is only on the south side of the center of circulation, and the storm still has a long way to go before attaining hurricane status. Dry air is intruding on the northwest side, and the upper level outflow is established only on the east side of the storm. Still, the overall satellite signature is rather ominous and impressive, with a large envelope of thickening clouds on the eastern side of the storm. The wind shear is still very low--about five knots, and expected to stay low. The last hurricane hunter mission left the storm at 4:30 pm EDT Sunday, so the exact strength of the storm is not known at this point. There is not another mission scheduled until 2 pm EDT today. The NOAA jet is scheduled to make its first flight Tuesday afternoon.

The forecast guidance still predicts that this will be Hurricane Wilma by Wednesday. Wilma will spend the next three days in a low-shear environment with water temperatures of 30 C (86 F), which should allow intensification into at least a Category 2 storm, perhaps even a Category 3. Wilma reminds me of Rita, which spent about three days trying to organize in the Bahamas before finally solidifying its inner core and rapidly intensifying. This storm may behave similarly.


Figure 1. Computer model tracks for Wilma.

Steering currents are expected to remain weak the next two days, and some erratic motion is possible. All of the forecast models predict a generally west or west-northwest motion over the next two days. However, this morning's southerly motion at 5 mph is something none of the forecast models have called for. This gives me some concern about this storm severely impacting Honduras and its neighboring Central American countries, particularly Guatemala, which is still reeling from the impact of Hurricane Stan. As Wilma grows in size, a continued southward motion may allow it to start pulling in a deep layer of moisture from the Pacific Ocean, which would trigger heavy rains over the regions of Guatemala and El Salvador hardest hit by Stan. These rains would probably be in the 3 - 5 inch range--nowhere near the devastating 15 - 25 inches seen from Stan, but still high enough to trigger new mudslides on the destabilized slopes of the steep mountainsides.

The computer models have been having huge difficulties with a weak trough of low pressure over the U.S. that may be able to pull Wilma northwards. Last night's 00Z (8pm) models runs of the five models we plot on our computer model tracking chart all failed to properly initialize this trough, calling for it to be weaker than is really is. This resulted in a set of model tracks with a much further west track for Wilma, bringing her into Belize or the Yucatan later in the week. This morning's 06Z (2am EDT) runs of the GFDL and GFS model did properly initialize this trough, and these new model runs now indicate a sharp turn to the northwest and north across western Cuba. Given that the models are not currently handling the southerly motion of the storm, I would be hesitant to believe this forecast yet. All the computer models were calling for a similar northward track for Hurricane Mitch in October 1998, and it ended up wandering south and getting stuck off of the coast of Honduras. However, a second much stronger low pressure system currrently bringing rain to southern California is expected to move east this week and push a trough far enough south to pull the storm northwards later in the week, if the current trough can't do the job. The west coast of Florida still appears likely to receive a hit from Wilma. The timing and severity of this blow are impossible to call at this point until Wilma starts her northwestward turn.

Elsewhere in the tropics, nothing else is happening. I'll be back with a update this afternoon about 4pm, when the latest set of model guidance will be in and the Hurricane Hunters will have visited the storm.

Stan revisited
The official death toll from Hurricane Stan in Guatemala is 654, with 830 people missing. Another 133 people have died in Mexico, El Salvador, Costa Rica, Nicaragua and Honduras, making Stan one of the 30 deadliest hurricanes in history. Over 3.5 million Guatemlans have been affected by the storm, with nearly 5,000 homes destroyed and hundreds of thousands damaged. Many corn, sesame and sorghum crops along the south coast were been destroyed, and Guatemala will need extensive long-term aid to recover from this immense disaster. The Guatemalan Red Cross has made available a way to donate online via the Active network (www.active.com). With the earthquake disaster in Pakistan and Hurricane Katrina competing for attention, donations are urgently needed in Guatemala.


Figure 2. View of the Lake Atitlan region of Guatemala, looking south towards the Pacific Ocean. The circulation of Hurricane Stan pulled a deep layer of moist air off of the Pacific Ocean, which triggered heavy rains of 15 - 25 inches. A huge mudslide roared down the slope of the Toliman volcano and buried the town of Panabaj, killing over 400 Guatemalans. Note the brownish deforested areas on the slopes of the Toliman volcano; the lack of vegetation on the slopes contributed to many of the mudslides from this disaster.


Jeff Masters