Weather Nerd

Omar, T.D. 16 form; both expected to strengthen

At 11:00 AM EDT, Tropical Depression 15 in the Eastern Caribbean became Tropical Storm Omar, and “Invest 99L” in the Western Caribbean became Tropical Depression 16. Both Omar and “proto-Paloma” are expected to strengthen.

Omar, in fact, “MAY BE STARTING A PERIOD OF RAPID STRENGTHENING,” according to the National Hurricane Center discussion. The official forecast calls for Omar to reach hurricane status at roughly the same time as it’s passing over the Virgin Islands. (The track has shifted east, away from Puerto Rico, and may shift further east if the computer models hold.)

Dr. Jeff Masters writes:

The storm is expected to drift southeastward until an upper-level trough of low pressure swings far enough south tonight to pull the storm northeastward towards Puerto Rico, the Virgin Islands, and the northern Lesser Antilles Islands. Variations in timings between the models have narrowed some, with landfall in the Virgin Islands, northern Lesser Antilles Islands, or eastern Puerto Rico expected sometime between Wednesday afternoon and Wednesday night. Heavy rains should spread into the islands tonight, generating additional rainfall totals of 5-10 inches. The eastern portion of the Dominican Republic will likely get 3-6 inches, and Haiti will escape heavy rains from the storm.

T.D. Sixteen, meanwhile, is expected to become Tropical Storm Paloma today or tomorrow. However, the intensity forecast is very uncertain because a great deal depends on the depression’s track. If the center stays just north of Honduras, as currently expected, strengthening is likely. In Dr. Masters’s words: “As long as the center remains over water more than 50 miles from land and does not stall out, intensification should occur.” But a slight deviation to the south would move T.D. 16 over land, and cut off the opportunity for intensification.

And deviations from the forecast are very possible. As Eric Berger notes, Sixteen “is quite interesting because the steering currents aren’t all that strong.” Some models even “bring the system into the Pacific Ocean and develop it there into a tropical storm.” So it’s anybody’s guess right now, though the most likely scenario is that proto-Paloma goes “north, then west into Belize.”

Masters writes:

The system will likely bring 5-10 inches of rain to northern Honduras today through Thursday, potentially causing flash flooding and destructive mudslides. Rain amounts of 2-4 inches are likely today over northeastern Nicaragua and the Cayman Islands. Heavy rains of 4-8 inches will likely affect Belize, northeastern Guatemala, and portions of Mexico’s Yucatan Peninsula tonight through Wednesday night. The heaviest rains will stay south of the resort areas of Cancun and Cozumel, though.

It currently appears that the center of 99L will stay close enough to the coast that the storm will not grow large and strong enough to tap into the Pacific Ocean as a major source of moisture. However, the counterclockwise flow of air around the storm is already strong enough that it is pulling in air from the Pacific over northern Costa Rica and Nicaragua. This moist flow of air should generate rain amounts of 2-4 inches today along the Pacific coasts of these countries. If 99L were to grow into a strong tropical storm, this moist flow of air would be capable of generating very dangerous rains in the 10-15 inch range along the Pacific coast of Central America.