TD 20 finally makes up its mind

Tropical Depression 20
The tropical disturbance in the western Caribbean Sea continues with its daily cycle of ups and downs, and finally hit enough of an "up" today to be classified as Tropical Depression 20. The amount of deep convection has increased to the highest level that we've seen yet, and now covers most of the western Caribbean Sea. An upper level outflow channel has opened to the north, and one can see high cirrus clouds streaming out to the north from the center of the depression. A few spiral bands have formed, and surface pressures continue to fall. The center of the depression is near buoy 42056 about 100 miles southeast of Cancun, Mexico. A hurricane hunter aircraft is on its way to investigate the system at 2 pm EDT afternoon.

The system is expected to cross the Yucatan Peninsula today and Sunday, so probably will not have time to strengthen into a tropical storm before then. Wind shear over the system is unchanged at 5 - 10 knots today, but after crossing the Yucatan, the shear is forecast to drop below 5 knots, and the system will have 36 hours or so to intensify over the warm 29 - 30C waters of the Gulf. I expect landfall as a Category 1 hurricane, or perhaps a strong tropical storm, on the Mexican coast south of Brownsville on Tuesday.

Hurricane Otis threatening Baja and Arizona
Hurricane Otis reached its peak intensity early this morning--a Category 2 hurricane with winds of 105 mph. Otis is expected to very slowly creep northwestward over cooler waters the next two days, and gradually weaken. By the time it takes a more northerly track and crosses the Baja Peninsula on Monday, Otis will probably be a strong tropical storm or weak Category 1 hurricane. Hurricane force winds extend outwards only 15 miles from Otis's center, so only a small portion of the coast will receive wind damage. Heavy rains of five inches or more will be the main problems with Otis, potentially triggering serious flash flooding in the desert mountains of Mexico--and by Tuesday, in Arizona.


Figure 2. Hurricane Otis.

TD 19
Tropical Depression 19 is far out over the Atlantic Ocean, about 600 miles west-southwest of the Cape Verdes Islands. The environment for strengthening is fair, and we will probably see this system become a tropical storm tonight. A hurricane seems unlikely, as this system is expected to move northwest or northward for the next five days into a region of increasing wind shear. It will be interesting to see if this storm or TD 20 wins the race to become Stan--loser gets the name Tammy.

Southeast U.S.
The global computer models are no longer forecasting tropical storm development near the Bahama Islands on Monday or Tuesday. Instead, they indicate that the favored genesis region may be the central or western Caribbean.

Hawaii
Flood watches are posted for all of the Hawaiian Islands as the moisture from Tropical Depression Kenneth moves over today. As yet, no heavy rains have impacted the islands.

Taiwan and China
Typhoon Langwang, a small but intense typhoon with 140 mph sustained winds, is headed towards a landfall on Taiwan Sunday. The upper-level outflow from the typhoon has degraded today, but there is no apparent wind shear affecting it, so landfall as a Category 3 or 4 storm is likely. Longwang is expected to weaken to a Category 1 storm after passage over the 10000 foot high mountains of Taiwan and continue on to strike mainland China on Monday.

Jeff Masters