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 , 13. syyskuuta 2009 klo 13:16 (GMT)
Hurricane Fred is dead, thanks to strong wind shear that finished tearing the storm apart yesterday. While the remains of Fred have generated a burst of heavy thunderstorms this morning, prohibitively high wind shear of 40 - 50 knots today through Monday will prevent regeneration, and should be able to completely disrupt the remnant circulation of Fred.
A tropical wave about 200 miles southeast of the Cape Verdes Islands, just off the coast of Africa, remains disorganized. This morning's QuikSCAT pass showed an elongated circulation, and one spot of 45 mph winds in the small clump of heavy thunderstorms on the south side of the circulation. The wave is under about 20 knots of wind shear, and may show some slow development beginning Monday, when the shear should drop below 20 knots. NHC is giving this system a low (less than 30% chance) or developing into a tropical depression by Tuesday.
A low pressure system that was over the Texas Gulf of Mexico coast has moved inland, and is not a threat to develop into a tropical cyclone. Tropical storm development is possible this week along a frontal zone stretching from Florida to the waters between the Bahamas and North Carolina. However, wind shear will be relatively high in this region, and anything that develops may end up being extratropical in nature.
Figure 1. The remains of Tropical Storm Fred (left) appear as a swirl of low-level clouds with a clump of heavy thunderstorm activity on the north side. A new tropical disturbance near the coast of Africa is disorganized, due to 20 knots of wind shear.
Twenty years ago on this date
On September 13, 1989, Tropical Storm Hugo continued its westward march at 20 mph towards the Lesser Antilles Islands. Shortly after midnight on the 13th, satellite analysts at the National Hurricane Center noted a Central Dense Overcast (CDO) of thick cirrus clouds was forming over the center. The CDO was evidence that Hugo was beginning to build an eyewall. The thunderstorms in the eyewall were now powerful enough to lift large amounts of moisture 45,000 feet high, where the stable air of the stratosphere lay. Unable to penetrate into the stratosphere, the air lifted by Hugo's thunderstorms was forced to spread outward into a thick, circular layer of cirrus clouds--the CDO--that hid the storm's core. The mystery of what was happening beneath the Central Dense Overcast became apparent a few hours later, when a murky eye appeared. At 8 am EDT on the 13th, the National Hurricane Center upgraded Hugo to hurricane status.
At NOAA's Office of Aircraft Operations--the hurricane hunting division of NOAA--we busily prepared for tomorrow's deployment to Barbados of both of our P-3 Orion hurricane hunting aircraft. There were dropsondes and Air-Expendable Bathythermographs to load, computer checks to make, and calibration data to load. We chatted excitedly about the new hurricane that looked like an excellent case study for the hurricane scientists. But there was also an undercurrent of uneasiness to our cheerful preparations. We knew that a Cape Verdes-type hurricane like Hugo that was still 2 - 3 days from the Lesser Antilles would probably kill a lot of people--perhaps even close to home, here in Florida.
In a letter I wrote that night to my soon-to-be-fiancee, Diane, in Michigan, I said: "Well, that dark enveloping death feeling is back again, much stronger than before. I know Hugo the hurricane will kill people and I feel it coming close to here".
Figure 2. GOES visible satellite image of Hurricane Hugo taken on September 13, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.
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