Two almost-tropical storms promise windy and wet weather for U.S. East Coast

A powerful extratropical storm (94L) with some tropical characteristics is bringing tropical storm-like conditions to the waters just offshore the U.S. coast, from South Carolina to Virginia. QuikSCAT data from this morning and last night (Figure 1) show that tropical storm-force winds of 40-50 mph cover a 400-mile swath of ocean just offshore the North Carolina coast. A Hurricane Hunter mission currently investigating 94L confirms that these winds continue, with a few spots of 55 mph winds. Visible satellite loops show a small amount of heavy thunderstorm activity near the center, with a long curved band of thunderstorms that arcs from the center northeastwards for several hundred miles. This configuration is characteristic of a subtropical or extratropical storm. NHC is currently judging the storm to be more extratropical, so it doesn't get a name. The difference is unimportant as far as the impact on the coast goes, since this storm will bring tropical storm force winds of 40-50 mph to the coast from northern South Carolina to Virginia today through Friday morning as it moves ashore. NHC is currently giving 94L a high (>50% chance) of becoming a subtropical storm by Friday. An Air Force Hurricane Hunter aircraft sent in a center fix at 9:48 am EDT, finding a central pressure of 994 mb and top surface winds of 54 knots (62 mph).


Figure 1. High-resolution QuikSCAT wind estimate from 7:05 pm EDT Wednesday 9/24/08. Browns and purples represent winds of tropical storm force (35 knots) or greater. Image credit: Brigham Young University.

The storm is affecting a wide area of coast from New York to South Carolina. Minor coastal flooding due to high winds is forecast as far north as New York City. The Onslow Bay buoy south of Wilmington, North Carolina, reported 13 foot waves and sustained winds of 45 mph at 8:20 am EDT. Wave heights in excess of 15 feet have been observed from Delaware to South Carolina, with the highest waves of 19 feet measured at the Virginia Beach Buoy 75 miles offshore from the Virginia/North Carolina border. Expect tide levels of 3-6 feet above normal along the coast, and rain amounts of 2-3 inches. Cape Hatteras, NC radar shows an extensive area of rain all along the coast. Thus far, (Figure 2) only 1-2 inches has fallen along the coast, but the heaviest rain has yet to move ashore. Rainfall amounts up to five inches (Figure 3) are likely from 94L as it sloshes northwards along the coast over the weekend.


Figure 2. Estimated rainfall from 94L.


Figure 3. Forecast rain amounts for the 5-day period beginning 8 am EDT Thursday 9/25/08. Image credit: NOAA.

Dominican Republic disturbance 93L
Tropical disturbance 93L is finally on the move, and is pulling away northwards from the Dominican Republic. Visible satellite loops show the classic signature of a tropical storm undergoing high wind shear--an exposed low-level circulation center, with all the heavy thunderstorm activity pushed over to one side by the shear. This morning's QuikSCAT pass found top winds of 45-50 mph in the region of heavy thunderstorms on the east side of 93L. A NOAA Hurricane Hunter plane is currently investigating 93L to see if it qualifies as a tropical storm.

The forecast
Wind shear remains near 20-25 knots, which is marginal for development. The current wind shear forecast from the SHIPS model relaxes the shear to 10-20 knots this afternoon through Friday, which should allow 93L to become a tropical storm. The most likely track for 93L, according to the computer models, is just east of Cape Cod, Massachusetts on Saturday afternoon, to a landfall in Nova Scotia on Saturday night or Sunday morning. Since the U.S. is on the thunderstorm-free weak side of the storm, it appears that Massachusetts and Maine will miss the highest winds. Sustained winds of 30-35 mph on Cape Cod and Nantucket are likely Saturday afternoon and evening from 93L. The storm's highest winds of 40-50 mph will affect Nova Scotia and New Brunswick Saturday night.

Elsewhere in the tropics
The UKMET and ECMWF models indicate the western Caribbean needs to be watched during the middle of next week for tropical storm development.

Links to follow
Cape Hatteras, NC weather
Duck, NC weather info and webcams fro the U.S. Army

The Hurricane Ike, "Presslord will wear a dress challenge" begins
Thanks go to everyone who has contributed to the portlight.org charity! We raised enough dough to send another truck with relief supplies to Winnie and Bridge City, Texas, where traditional relief efforts have fallen short. Wunderground member Presslord (AKA Paul Timmons, Jr.), who is coordinating this effort, has announced that if we raise an additional $10,000 mark, he will pose in a dress for our wunderphoto gallery. I know I personally will be contributing to help decorate our wunderphoto gallery (but more so to help out the people of Winnie and Bridge City!) We're up to $1500 so far.


Figure 4. The town of Bridge City was inundated with a massive storm surge even though it was far displaced from Ike's landfall point. This speaks to just how massive Ike was. The people of Bridge City, Winnie, and other small towns in Ike's path will need help for a long time to come: www.portlight.org. Image credit: Storm Junkie.

Your contributions do make a difference, and you can read more about the effort at at stormjunkie's blog.

Jeff Masters