Tropical weather analysis - October 11, 2010

Paula

Tropical Storm Paula formed this afternoon in the western Caribbean, east of Honduras. As of the latest NHC advisory (11:00 PM EDT), here is the latest information on Paula:

Wind: 70 mph, with higher gusts
Movement: NW at 10 mph
Pressure: 994 mb
Location: 16.8N 84.6W
Category: Tropical storm

Infrared satellite imagery indicates that Paula is a healthy and intensifying tropical cyclone, with very cold convection over the center and what appears to be the early stages of an eyewall wrapping cyclonically around the center. However, an eye or warm spot is not yet evident using conventional satellite imagery. Unfortunately, there have been no recent microwave satellite passes over the center of the cyclone to confirm this suspicion.

Regardless, it is quite obvious that Paula is an intensifying tropical cyclone. The storm has managed to develop a well-defined poleward and equatorial outflow channel, namely along the northern and western semicircles. Indeed, outflow is also becoming apparent to the south of the center. It remains restricted to the east due to weak southeasterly shear induced by an upper-level high pressure system centered near northwestern Colombia.

Upper-level winds appear favorable for Paula to continue intensifying over at least the next 48 hours. Thereafter, increasing southwesterly to southerly vertical shear will begin to impinge upon the system. This, along with a very dry airmass across the Gulf of Mexico, should begin to weaken Paula after 48 hours. The GFDL brings the system to 75 kt near the northeastern Yucatan Peninsula in 36 hours. While this track seems a tad too fast, the model certainly has the right idea in forecasting such a degree of intensification. In fact, for once, I think the GFDL is being too conservative. I'll go a bit higher, and forecast Paula to become an 85 kt Category 2 hurricane in the western Caribbean in about 48 hours.

It is certainly not out of the question that Paula could become a major hurricane over the next two days or so, especially if current trends continue.

Paula is being steered generally NW by a low- mid-level ridge to the east. It is possible, based on analysis of said imagery along with water vapor imagery, that Paula could turn a little to the right over the next couple hours before bending back to a straight NW course.

In the short-term, Paula should continue moving in this general direction, bringing the center in the general direction of the Yucatan Peninsula in the next 36-48 hours. Thereafter, the track forecast becomes quite complicated, and is dependent entirely upon the strength and amplification of a deep-layer trough forecast by the models to move across the southeast United States.

Depending on the model of your choice, the effects of this trough on Paula's motion varies. Some move the cyclone quickly poleward as Paula comes underneath the influence of the deep-layer westerly flow associated with the aforementioned trough, quickly ejecting it toward western Cuba by about 48 hours.

Others foresee Paula slowing to a crawl and either meandering in the western Caribbean Sea for several days, or moving very slowly eastward, never to leave the Caribbean throughout the forecast period (five days).

Right now, my current thinking is that, based upon current intensification trends and water vapor analysis, Paula will move a bit more poleward than some of the models are thinking, as a well-defined weakness is evident at 400 mb due to a shortwave trough currently moving across the Texas/Louisiana area.

This trough should drop a bit more southward over the next 12-18 hours as a well-defined upper-level low located across the central plains has moved quite far to the southeast over the last several hours. Since Paula is intensifying, it will be strong enough to feel this deep-layer trough. And, as a consequence, move more poleward.

For my forecast track, out of respect for the usual reliability of these two global models, as well as given current trends, and of course, the ever-present uncertainty in long-range weather forecasting, particularly with systems such as Paula, I will compromise between the faster GFS and the slower ECMWF.

This comes out to a forecast of Paula moving NW over the next 36-48 hours, toward the eastern Yucatan Peninsula, and then slowing down a bit and moving very slowly eastward, possibly just north of due E during the remainder of the forecast period.

This track is highly uncertain until the synoptic scale situation becomes clearer. Given the uncertainty, interests in Honduras, Belize, the Yucatan Peninsula, Jamaica, the Cayman Islands, western Cuba, south Florida, and the western Bahamas should closely follow the progress of Paula over the next several days.

In the meantime, heavy rainfall is possible across portions of Honduras, Nicaragua, Jamaica, Belize, the Cayman Islands, the Yucatan Peninsula, and western Cuba over the next several days. These rains have the potential to produce life-threatening flash floods and mudslides across these areas.

Watches and warnings

A HURRICANE WARNING IS IN EFFECT FOR...
* THE COAST OF MEXICO FROM PUNTA GRUESA NORTHWARD TO CABO CATOCHE...
INCLUDING COZUMEL

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* THE COAST OF HONDURAS FROM LIMON EASTWARD TO THE
HONDURAS/NICARAGUA BORDER...INCLUDING THE BAY ISLANDS
* THE COAST OF MEXICO FROM CHETUMAL NORTHWARD TO SOUTH OF PUNTA
GRUESA
* THE COAST OF MEXICO FROM CABO CATOCHE TO SAN FELIPE

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* THE COAST OF BELIZE