Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters from 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather
By: Dr. Jeff Masters , 2:42 PM GMT on November 05, 2008
An area of disturbed weather (93L), a few hundred miles east of the coast of Nicaragua, continues to slowly organize. This morning's QuikSCAT pass revealed that the circulation center is broad and ill-defined, and the satellite noted winds of about 30 mph in the heaviest thunderstorms. Visible satellite images show that heavy thunderstorm activity has shown a moderate increase in intensity and areal coverage this morning. An upper-level outflow channel has opened to the north, but there is no evidence of low-level spiral bands forming yet.
Figure 1. Current satellite image of 93L.
Wind shear has dropped to a low 5-10 knots this morning, and is expected to remain in the low to moderate range, 5-15 knots, over the next three days. The phase of the Madden-Julian Oscillation has changed to positive over the Western Caribbean over the past few days, and this should act to reduce wind shear and enhance the storm's updrafts and instability. Nearly all of the tropical cyclones that have formed in the Atlantic this season have formed under a positive Madden-Julian phase. Water temperatures are warm, 29.5°C, and this warm water extends to great depth. These are favorable conditions for intensification, and both the GFDL and HWRF models predict 93L will become a hurricane, with the HWRF predicting a major hurricane. The SHIPS intensity model is less aggressive, predicting a strong tropical storm with 65 mph winds by Saturday. I give 93L a 50% chance of eventually becoming a hurricane, and a 20% chance of becoming a major hurricane. These odds will increase tomorrow if 93L can avoid passing close enough to the northeast coast of Nicaragua for significant weakening due to land interaction. This storm has the potential to imitate Hurricane Michelle of 2001. Michelle formed in the same region at the same time of year, and took just three days to intensify from a tropical depression to a Category 4 hurricane. Michelle made landfall in central Cuba as a Category 4 hurricane, then weakened to a Category 1 hurricane as it passed through the Bahamas.
A slow north-northwest motion to a point just offshore the Nicaragua-Honduras border is likely for 93L through Thursday. At that time, a strong trough of low pressure will be approaching the U.S. East Coast. Only one major model, the NOGAPS, predicts that this trough will be too weak to turn 93L northwards, and I am discounting this solution at present. The other five major models agree on a northward motion, bringing 93L near the Cayman Islands or western Jamaica on Saturday, followed by a northeast turn. On Sunday morning, 93L should make landfall in Western Cuba, then pass through the central or eastern Bahamas on Sunday afternoon as it accelerates to the northeast.
Given the current increasing trend in organization, I believe 93L will become a tropical depression tonight or Thursday morning. NHC is giving 93L a high (>50% chance) of developing into a tropical depression by Friday morning. There is the potential that 93L could enter a period of rapid intensification on Saturday, bringing it to hurricane status. Residents of the Cayman Islands, Jamaica, and western Cuba should anticipate the possibility of a hurricane affecting them Saturday and Sunday. If 93L crosses Cuba as expected and moves into the Bahamas, it will weaken due to the interaction with land and the presence of very high wind shear of 30-50 knots just north of Cuba. These effects should weaken the storm by at least 40 mph before it passes through the Bahamas. The HWRF model predicts 93L could be a Category 2 hurricane in the Bahamas, but I think a tropical storm is more likely.
Northeastern Nicaragua and northeastern Honduras are at risk of heavy rains from 93L today through Friday morning. Total rainfall amounts of 4-8 inches are likely. Rains of 1-2 inches fell last night in Jamaica, and heavy rains of 4-8 inches should affect Jamaica and the Cayman Islands Thursday through Saturday. The first Hurricane Hunter flight into 93L is scheduled for this afternoon.
Links to follow
Wundermap for 16N 83W
I'll have an update this afternoon when the new model runs are in and the Hurricane Hunter data is available.
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