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 , 1:28 PM GMT on September 12, 2009
Tropical Storm Fred has been ripped apart by wind shear, as strong southerly winds of 20 knots have removed all of Fred's heavy thunderstorms, leaving only a naked low-level swirl of clouds. Wind shear of 20 - 40 knots will continue today through Monday, and Fred should dissipate by Sunday night. Due to the continued strong shear expected over Fred the next four days, it is unlikely there will be anything left of the storm to regenerate from once the remains reach an area with moderate wind shear five days from now.
Figure 1. Tropical Storm Fred (upper left) appears as a swirl of low-level clouds with no heavy thunderstorm activity in this morning visible satellite image. A new tropical disturbance (right) near the coast of Africa is disorganized, due to 20 - 30 knots of wind shear.
Elsewhere in the tropics
A large tropical wave that emerged from the coast of Africa Thursday is very disorganized. The wave as yet does not have much in the way of heavy thunderstorm activity associated with it, and wind shear is high, 20 - 30 knots. By Monday, the shear may drop below 20 knots, allowing some slow development. The GFS model has backed off on its prediction that this wave would develop into a tropical depression.
A low pressure system is over eastern Texas and the adjoining waters along the Texas Gulf of Mexico coast. This low is under high shear, about 25 knots, and is not tropical. Shear is expected to remain high, 20 - 30 knots, over the next five days. The low should remain non-tropical during this time, but will bring much-needed heavy rains to drought-stricken south Texas. Heavy rains in excess of five inches have occurred over portions of Texas, Oklahoma, and Louisiana from this low, and flash flood watches have been posted for a large sections of these states.
Over the next few days, we should also be alert for tropical storm development along a frontal zone stretching from the Gulf of Mexico waters offshore the western Florida coast, across the Florida Peninsula, 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 2. Total rainfall from the Austin, TX radar from the low pressure system over coastal Texas.
Twenty years ago on this date
On September 12, 1989, Tropical Storm Hugo, still far out at sea in the middle Atlantic, continued to grow more organized. Heavy thunderstorms thickened near the storm's center and in four prominent spiral bands. Updrafts from the intense thunderstorms near the storm's core began reaching the base of the stratosphere, creating high cirrus clouds that an upper-level anticyclone over the storm carried away. By nightfall, Hugo had intensified to a strong tropical storm with 65 mph winds. Now three days from the Lesser Antilles Islands, the storm continued to churn westward across the open Atlantic at 20 mph.
At NOAA's Miami-based Office of Aircraft Operations--the hurricane hunting division of NOAA--my boss, Jim McFadden, called me into his office. My fellow flight meteorologist, Jack Parrish, was also there. "We've got a planned two-plane deployment to Barbados on the 14th", Jim told us. "Frankly, if this storm wasn't named after the director of AOML, we wouldn't be going. It doesn't look too impressive right now." (AOML was NOAA's Atlantic Oceanographic and Marine Laboratory, which supervised research flights by NOAA's hurricane hunter aircraft, and Hugo Bezdek was the director). We discussed the possible missions, and agreed that regardless of Hugo's strength, we should be flying it, since we had used up very few of our allotted flight hours for the year. Jack and I would be in charge of coordinating the missions on the two aircraft. It would be my first hurricane flight of what had been a very slow season so far. I was excited to be going to Barbados, an island I had never been to. The as-yet unimpressive Tropical Storm Hugo did not give me any concerns about a possible rough ride.
Figure 3. AVHRR visible satellite image of Tropical Storm Hugo taken on September 12, 1989. Well-developed low-level spiral bands are apparent, and high cirrus clouds denoting upper-level outflow are visible on three sides. Image credit: Google Earth rendition of the NOAA HURSAT data base.
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