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Henri hanging on in the face of high wind shear

By: Dr. Jeff Masters, 1:31 PM GMT on October 07, 2009

Our second October surprise this week in the Atlantic, Tropical Storm Henri, continues to defy 25 knots of wind shear. Henri has strengthened to a 50 mph tropical storm this morning, but wind shear is keeping the storm's heaviest thunderstorms confined to the southeast side of the circulation. Satellite loops show that Henri's low level center is exposed to view, and that the heavy thunderstorms may be retreating from the center, a sign that shear could be starting to rip the storm apart. This morning's QuikSCAT pass missed Henri, and last night's pass showed winds of 40 - 45 mph.

All of the reliable global computer models show weakening and dissipation of Henri by Thursday, due to high wind shear. The official NHC forecast goes along with this scenario, and I'll go along, given the unanimity and persistence of the models in forecasting this. Wind shear in the vicinity of Henri's remains is predicted to fall to the moderate range by Saturday, so we will have to be concerned with regeneration after Henri dissipates. It appears likely that moisture from Henri will affect Puerto Rico by Friday, the Dominican Republic on Saturday, and Haiti on Sunday. It is too early to tell if Henri's remains will be capable of causing flooding rains in these regions.

Figure 1. Morning satellite image of Henri (top) and a new tropical wave we're watching (bottom). The tropical wave south of Henri, just off the coast of South America, has become more organized this morning. This wave is under about 10 knots of wind shear, but is too close to the Equator to be able to take advantage of the Earth's spin to help it spin up into a tropical depression very quickly. NHC is giving this disturbance a low (less than 30% chance) or developing into a tropical depression by Friday.

Pacific typhoons
In the Philippines, Tropical Storm Parma completed its second traverse of the Philippines' Luzon island, and has emerged over the Philippine Sea to the east of the country. Parma is expected to reverse course and cross Luzon a third time over the next three days. Parma is expected to dump another 1 - 2 inches of rain today on northern Luzon.

Typhoon Melor has weakened to a Category 2 typhoon with 100 mph winds, thanks to high wind shear and cool ocean waters. The typhoon should weaken to Category 1 strength before making landfall near 3am Japanese time on the main island of Honshu, just south of Osaka. Melor will probably bring sustained winds of 40 mph to Tokyo. You can follow the landfall of Melor with our interactive wundermap for the region. Several coastal locations are already reporting sustained winds near 40 mph.

Some tropical weather for England
The remnant circulation of Tropical Storm Grace made landfall in Southwest England last night. Grace's remains brought sustained winds of tropical storm force--41 mph--to one buoy off the coast, and 38 mph to the Sevenstones Lightship buoy.

Figure 2. The remnant circulation of Tropical Storm Grace scoots by to the south of Ireland in this visible satellite image taken at 1pm EDT 10/06/09. Image credit: UK Met Office.

I'll have an update late this afternoon.

Jeff Masters


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