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98L and Fred-ex pose little threat

By: Dr. Jeff Masters, 3:21 PM GMT on September 20, 2009

A tropical disturbance (98L), is located midway between Africa and the Lesser Antilles Islands. This disturbance has lost most of its heavy thunderstorm activity over the past day. Last night's QuikSCAT pass showed an elongated circulation, with top winds around 30 mph. Wind shear is moderate, 10 - 15 knots, and Sea Surface Temperatures are 28°C, which is about 2°C above the 26°C threshold needed to support a tropical cyclone. There is a large amount of dry air to the north and west of 98L, and this dry air has been instrumental in disrupting development of 98L over the weekend.

Wind shear over 98L is expected to remain in the moderate range, 10 - 15 knots, through Tuesday evening, according to the SHIPS model. This may allow the storm to organize into a tropical depression, assuming it can fight off the dry air that surrounds it. Tuesday through Thursday, the SHIPS model predicts shear will increase to the high range, 20 - 25 knots, so it is unlikely 98L will become anything stronger than a weak tropical storm over the coming 5-day period. The models predict that a strong trough of low pressure will turn 98L to the northwest and then north beginning on Monday, with the result that 98L misses the Lesser Antilles Islands by at least 500 miles. NHC is giving 98L a medium (30 - 50%) chance of developing into a tropical depression by Tuesday. It does not appear that 98L will ever threaten any land areas. The GFDL and NOGAPS models develop 98L into a tropical storm; the other models do not.

Figure 1. Morning visible satellite image of Fred-ex (located at the tail end of a cold front draped over the Atlantic), and 98L.

The remains of Hurricane Fred are still spinning away about 600 miles east of the Georgia-Florida border. Fred-ex's circulation has become ill-defined over the past day, and there has been no increase in heavy thunderstorm activity. High wind shear of 20 - 30 knots is affecting the storm, and there is also quite a bit of dry air interfering with development. The high wind shear and dry air will continue to affect Fred-ex over the next three days, as the storm moves west-northwest at 10 mph. Most of the models show the moisture from Fred-ex moving ashore between northern Florida and North Carolina Tuesday or Wednesday. None of the models develop Fred-ex, and I'm not expecting it to cause any flooding problems when it moves ashore.

Twenty years ago today
On September 20, 1989, Hurricane Hugo continued its steady northwest march at 15 mph towards the Southeast U.S., brushing the Bahama Islands along the way. Wind shear diminished, allowing the hurricane to intensify back to a major Category 3 hurricane with 115 mph winds. Hurricane watches and warnings had not yet been posted for the U.S. coast, but at noon on September 20, Mayor Riley of Charleston went on the air, telling residents of the city that Hugo was a killer. There was a very good chance that Hugo would be South Carolina's worst disaster this century, he said, with a storm surge up to fifteen feet high. Now, while the weather was good and the storm still far away, was the time to board up and get out.

Figure 2. AVHRR visible satellite image of Hurricane Hugo taken on September 20, 1989. Wind shear had diminished, allowing Hugo to intensify to a Category 3 storm with 115 mph winds. Image credit: Google Earth rendition of the NOAA HURSAT data base.

South Carolinans paid attention. Within an hour, residents jammed hardware stores and supermarkets. Traffic on roads away from the coast swelled as people scrambled to flee the arrival of the first major hurricane to strike South Carolina in thirty years--since Category 3 Hurricane Gracie of 1959 slammed into the coast south of Charleston.

At 6 pm, it became official: the Southeast U.S. coast from St. Augustine to Cape Hatteras had been placed under a hurricane watch, meaning that hurricane conditions could be expected within 36 hours. The torrent of evacuees leaving the coast swelled, reaching a million people in all.

In the U.S. Virgin Islands, the aftermath of Hugo became desperate as widespread looting erupted on St. Croix, forcing President Bush to send 1,100 troops. Wunderground member Mike Steers was there, and relates this story: "Surviving the aftermath was the real challenge. The lack of power, water, communications of any kind, and the crime and looting was the real test. After about a week of digging out of the remains of the house and neighborhood I was able to venture out on my motorcycle to see what had become of my job. On the way, I personally witnessed the looting and lawlessness. I even saw a National Guard truck backed up to what was a appliance store and the guardsmen were helping themselves to washers and dryers. Never mind that there was no power to run them. When I got to the seaplane ramp, I saw the total destruction that is depicted in one of the photos I sent. On my way home, there was a small local grocery store I had usually gone to, and I was going to stop in and see how the owners were doing. There was a band of youths in the process of carrying out everything that was not nailed down. From the back, out ran a rastaman with a machete saying he wanted my motorcycle. Needless to say, I gunned it and got back to my house as soon as possible. My neighbors and I set up our own armed 24-hour security checkpoint to protect ourselves. It was about a week later that the first of the giant C-5s flew over, sent by President Bush to start to restore order..."

Figure 3. Newspaper headline from the Virgin Islands Daily News after Hurricane Hugo, detailing the looting problems on St. Croix. Image scanned in by Mike Steers.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.