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 , 21:33 GMT le 04 novembre 2009
Tropical Storm Ida has arrived, the ninth named storm of the 2009 Atlantic hurricane season. Visible satellite loops show that Ida continues to steadily organize, with surface spiral banding and upper-level outflow now obvious over the northern portion of the storm. An Air Force hurricane hunter aircraft is in the storm, and found a large area of surface winds in the 45 - 50 mph range, with a smaller area of 60 mph winds, prompting NHC to upgrade the storm.
Figure 1. Afternoon satellite image of Ida.
Ida is currently under low wind shear, 5 - 10 knots, and shear is expected to remain in the low to moderate range in the Western Caribbean for the remainder of the week. Sea Surface Temperatures (SSTs) are 29°C and the Tropical Cyclone Heat Potential is about 40 kJ/cm^2, which is enough energy for a hurricane to form, if the center remains over water long enough. The Western Caribbean is plenty moist, and dry air is not an issue for Ida. Ida is currently too small to be affected by tropical disturbance (Invest 96E) 500 miles to its west, over the Eastern Pacific.
The forecast for Ida
The 1 - 3 day forecast for Ida has come into better focus now that the storm has formed, and models have come into better agreement. The current west to northwesterly motion of Ida should carry it inland over northeastern Nicaragua early Thursday morning. Ida is too small to tap the Pacific as a source of moisture, and it is just the northeastern portions of Nicaragua and Honduras that need to be concerned with heavy rains and mudslides. With Ida expected to spend a full two days over land, rainfall amounts of 10 - 15 inches over northeastern Nicaragua and Honduras will likely make Ida the deadliest storm of the 2009 Atlantic hurricane season. There is a medium chance (30 - 50%) that Ida will dissipate while over land. If Ida survives the crossing and emerges into the Western Caribbean on Saturday, low to moderate wind shear and warm waters await it, and strengthening is likely. An extratropical storm is forecast by GFS and ECMWF models to form in the Gulf of Mexico's Bay of Campeche on Saturday, and the counter-clockwise flow of air around this storm may propel Ida northwards into the Gulf of Mexico by Monday. However, both of these models show a high pressure ridge building in and forcing Ida southwards, back into the Caribbean, by the middle of next week. The long term fate of Ida, should it survive the crossing of Nicaragua and Honduras, remains murky.
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