No tropical depression yet near Jamaica

The broad 1005 mb low pressure area centered just south west of the island of Jamaica has become better organized this morning. The areal coverage of the deep convection continues to increase. Some weak upper-level outflow exists on the west and north sides of the system, and a weak upper level anti-cyclone has developed on top. Wind shear is still decreasing, and is now about 5 knots over the storm. All signs point to development of a tropical depression by Sunday, and a tropical storm by Monday. One complicating factor may be the presence of Jamaica so close to where the center is trying to form. This may slow development by half a day or so at most, since Jamaica is a relatively small island. A hurricane hunter aircraft is scheduled to investigate the system at 4 pm EDT today.

Global computer models forecast that the shear will continue to remain low the next several days over the western Caribbean, where the disturbance is expected to remain. If the system can remain in the western Caribbean for five days, the chances of it growing to hurricane strength are good. The latest GFDL model run even suggests that major hurricane status is possible.


Figure 1.
Early model tracks for the Jamaica disturbance.

Steering currents are expected to remain weak the next five days, and the computer models have a variety of solutions, so pick one:

GFS model: A weak tropical storm with a slow WSW motion, with landfall in Belize in seven days.

UKMET model: A hurricane with a slow WNW motion, winding up in the Yucatan Channel between Cuba and the Yucatan Peninsula in seven days.

NOGAPS model: Same as GFS, a weak tropical storm with a slow WSW motion, and a landfall in Belize in seven days.

GFDL model: A hurricane that moves WSW and stays in the Western Caribbean the next seven days.

Canadian model: Slow WSW motion as a tropical storm, then sharp northward turn and intensification into a hurricane as it crosses Cuba and passes just offshore Miami through the Bahama Islands.

If this system does eventually affect the U.S., the most likely target would be the Florida Keys or west coast of Florida, as there are many troughs of low pressure whizzing by that would grab this system and steer it to the northeast once it gets far enough north.

Cape Verdes tropical disturbance
A tropical disturbance about 500 miles west of the Cape Verde Islands is experiencing high wind shear that will prohibit development for the next few days as it tracks west-northwest over the open ocean.

Katrina's winds revisited
In my last blog entry on this subject, we discussed the Florida Sun-Sentinel article commenting on new findings that indicate Katrina was only a Category 3 hurricane at first landfall near the mouth of the Mississippi, and a Category 1 hurricane over New Orleans. The article was rather imprecise in its use of the Category system for ranking hurricanes, and I interpreted the article to mean that Katrina was a Category 1 at landfall in Mississippi. Upon re-reading the article, I think what they were trying to say was that Katrina had Category 1 force winds over New Orleans, not that the storm itself was a Category 1. As several of you have pointed out, it is pretty difficult to have a hurricane with a 927 mb pressure (Katrina's pressure at landfall in Mississippi) with just Category 1 winds. Katrina was a least a strong Category 2, and perhaps a weak Category 3 hurricane at landfall in Mississippi. While Katrina did have unusualy high winds aloft compared to surface winds (which NHC noted on one of their discussions during the storm), this difference was not enough to make Katrina a Category 1 hurricane at landfall in Mississippi. Sorry for sowing the confusion!

My next post will be Saturday afternoon about 5pm.

Jeff Masters