Thursday, July 25, 2013

Tropical Storm Dorian Threatening United States

Tropical Storm Dorian has increased the threat of making a landfall on the United States overnight, as computer models suppress the storm to the south in an effort that could draw the system into the Gulf of Mexico.

[Image Removed]

Latest model guidance has a fairly straightforward solution this morning. TS Dorian is favored to continue on a west-northwest path, staying just north of the Caribbean in coming days. As it approaches the waters north of Cuba, some models start to curve the system northward in the beginning stages of what would have Dorian make a u-turn and move back out to sea. However, as many GFS Ensemble members are showing now, some other models hold off on this u-turn plan and continue on a WNW path. This is a new development, and one we need to discuss.

This is the current atmospheric flow chart for TS Dorian. The system is seen just below that big anticyclone of white circles as a small red area in the bottom right corner of the image. If we follow the white lines in and around TS Dorian, we see a WNW track is indeed favored over the next couple of days, as the massive anticyclone to Dorian's north suppresses the system and pushes it along.

This is where things get interesting. On the GFDL model's forecast for the same atmospheric flow level in the image above (valid for July 29), we see Dorian ENE of Cuba, shown as a green and blue swath in this image. But look where the arrows directly west of the green area are pointing: west. Some arrows on the northern fringes of Dorian are going for that u-turn pattern, but the arrows (streamlines) in the center of Dorian are the most influential on its path, and call for a continued WNW movement. If we were to go into the future another 24 hours, we would see that this westward trend continues, and Dorian would be headed for not only Florida, but possibly the Gulf of Mexico.

This all depends on just how the major anticyclone in the second image operates. This continued WNW path would depend on if more anticyclones are able to suppress the storm into taking a Florida or Gulf-bound route, as the above forecast is currently showing.

The two most prevalent tracks I see involve the U-turn idea, where Dorian would curve north and out to sea before hitting Florida, although greatly impacting the Bahamas, and a track where Florida is hit, but not by a direct landfall. Landfall then occurs on any land from Mississippi to the Florida Panhandle, as a u-turn curve pattern takes place. Regardless of the track, the Bahamas will experience tropical activity if the latest forecasts hold up (which I think they will).


No comments: