Tropical Outlook

T.D. 3 formed last night off the coast of South Carolina and continues to spin about 100 miles east of Charleston. This was a classic case of tropical development in the proximity of a dying frontal boundary. For the past few days, thunderstorms persisted in advance of the decaying front over the warm waters of the Gulf of Mexico and the Atlantic. With wind shear relaxing, this was an ideal breeding ground for tropical development, and it certainly doesn't surprise me to see this system spin-up.

The model guidance suite agrees that this system stays just offshore of the U.S. The GFDL, however, forecasts T.D. 3 to flirt with the Outerbanks of North Carolina Sunday evening. It appears that the NHC is placing the track between the other computer models and the GFDL. I actually like their track given the position of the Bermude High. Given this track, most of the heavier squalls and strong winds should be confined to the immediate coastline and/or remain just offshore.

With shear remaining low (<10 knots) and warm water temperatures (82-84 F), this system should easily acquire tropical storm status. In fact, this system will probably be named by the end of the day. My biggest disagreement with the NHC's forecast is the conservative intensity forecast for T.D. 3. I feel that this system could wind up being a fairly strong tropical storm within a couple of days. Afterwards (Tuesday and on), increased wind shear associated with a trough will likely limit further strengthening.

A menacing looking tropical wave is moving through the Western Caribbean this weekend. This is the same wave that has been monitored by the NHC for several days but has yet to develop. It moved through the graveyard of the Eastern Caribbean a few days ago and survived. Air Force planes found a broad center of circulation a few days ago but not tight, closed circulation. As it is, it still remains a strong easterly wave. It's currently being impacted by wind shear associated with an upper low over Cuba. The northern part of the wave is experiencing about 20 knots of shear while the southern end is experiencing about 15 knots of shear.

Until this upper low weakens and moves out of the way, development should be inhibited. However, models are in agreement with weakening the upper low and moving it out of the path of the tropical wave by Sunday. When this happens, development will become increasingly likely with very warm water and low shear in its path. Given the upper low in its path right now and the eventual breakdown of the Bermuda High next week, this system does pose a threat to the U.S. late next week.

I think there is a strong likelihood this system will develop and could strengthen rapidly once in the Gulf of Mexico. A possible caveat does include any interaction with land, which would weaken the system. Still, I think there is a real possibility of Texas or Mexico dealing with a strengthening system at landfall late next week.

These slow organizing systems that develop closer to the U.S. worry me much more than the long-track Cape Verde systems. Why? Most importantly, the water is usually much warmer closer to the U.S. and increases the potential for rapid intensification. Two, these systems don't have a week for complex interactions to disrupt the circulaton. They usually intensify quickly and are usually intensifying at landfall. Three, when they develop close to the U.S., they are almost guaranteed to hit some land mass. A large majority of the quickly developing Cape Verde systems usually re-curve out to sea and only pose a threat to shipping. I'll be keeping a close eye on this system over the next several days.

What is left to say about Hurricane Bertha? Wow! She continues to persist in the open Atlantic and is still a tropical cyclone. She has been around for 16 days and she shattered the old record for longest July storm (12 days). Her time is almost up, and she should transition to an extratropical cyclone by the end of the weekend. It even looks like she may take aim at Iceland early next week!

Elsewhere in the tropics, things are quiet, but that may not last long. A very strong wave is poised to merge off the coast of Africa next week with several other waves to follow. It's still a bit early to be concerned about Cape Verde systems, but Bertha showed anything is possible this year. Any system that emerges off the coast at a latitude lower than 13 degrees N should have warm enough water to develop. I still think the Cape Verde systems will be more of a threat in a couple of weeks.