Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.
By: Dr. Jeff Masters , 3:45 PM GMT on October 08, 2005
Subtropical Tropical Depression 22 formed from a non-tropical low 300 miles southeast of Bermuda. This low is not entirely tropical in nature--there are some substantial horizontal changes in temperature like one finds in regular mid-latitude low pressure systems, and the maximum winds are found in a curved band to the storm's northeast, well away from the center. Storms of this nature are called subtropical. If this system continues to intensify and attain maximum sustained winds of 40 mph, it wil be named Subtropical Storm Vince. See the Hurricane FAQ for more information on subtropical storms.
Wind shear over the system is about 10 knots today, which is slightly favorable for tropical storm development. However, in the noon to 1 pm EDT time frame, wind shear from the southeast increased and blew the deep convection away from the center, which was exposed. The center re-formed to the northwest under the deepest convection, and now TD 22 is looking more tropical, with the circulation center positioned beneath the main convection. Wind shear is expected to fluctuate around 10 knots through Monday, which should allow some slow intensification. After that time, higher shear is expected. TD 22 is over water of 26 - 27C, which is just warm enough to support a tropical storm. However, its current track will push the storm just south of Bermuda on Sunday, where water temperatures fall below 26C, which may cause some temporary weakening before the waters warm up again. By Tuesday, when the storm is expected to turn north, water temperatures again fall below 26C, and slow weakening should result. However, the forecast beyond three days has a higher than usual level of uncertainty, because most of the computer models are forecasting that a second tropical cyclone may form behind TD 22 by Monday and steer the storm more to the west. In any case, intensification beyond a strong tropical storm is unlikely given the marginal sea surface temperatures and wind shear.
Figure 1.Sea Surface temperatures below TD 22 are just barely high enough to support a tropical storm. The blue color (26C) is the dividing line between temperatures that are warm enough and not warm enough to support a tropical storm.
What's behind TD 22?
The tropical disturbance we've been following about 750 miles east of the Lesser Antilles Islands has grown disorganized today, and now has 20 knots of shear over it. Development is not expected through Sunday of this system.
Figure 1. Model tracks for suspect area east of the Lesser Antilles Islands.
Stan now ranks as one of the 30 most deadly hurricanes of all time, with over 1500 deaths caused. The grim task of recovering bodies in Guatemala continues today, where the entire town of Panabaj in western Guatemala was buried in a landslide, killing all 800 residents. Another 600 died in mudslides elsewhere in Guatemala. The storm also killed 67 people in El Salvador, 24 in Mexico and 11 in Nicaragua. Hundreds more are missing and presumed buried under landslides near Lake Atitlan in Guatemala. In a freakish double whammy, a magnitude 5.8 earthquake hit Guatemala Friday, causing additional damage, but no deaths. Also bizzare is the volcanic eruption that occured during the height of Stan rains in El Salvador on October 1. The eruption killed two and injured dozens. When you add these events to the magnitude 5.4 earthquake that rocked Taiwan at the height of Tyhoon Longwang on October 1, one might wonder if there is a connection between seismic activity and hurricane activity! There isn't.
Historically, 20% of all Atlantic tropical storms have occured in the month of October. In a nomal year, this means we can expect two tropical storms, one of which becomes a hurricane. According to Dr. Bill Gray's October 2005 hurricane forecast issued on October 3, this year we can expect an above average October, with three tropical storms, two of which become hurricanes--one of those a major hurricane. We have already had two named storms this month, Stan and Tammy. Vince seems like a good bet by Sunday. Long range computer model forecasts continue to show that conditions for breeding tropical storms will be excellent until at least the last week of October, so two more named storms--Vince and Wilma--will likely result by October 21. This would tie 2005 with 1933 as the busiest hurricane season ever. It is interesting to note that in 1933, the final three storms all showed up after October 25. If 2005 follows a similar pattern, we'll have Alpha, Beta and Gamma in addition to Vince and Wilma before it's all over. Dr. Bill Gray is not forecasting any November storms to form. However, we should get at least one, given the current pattern and continued above-normal sea surface temperatures over the Atlantic.
Figure 2. Typical tropical storm formation areas for October.
The next update will be Sunday around 11 am, or later today if something interesting happens.
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