Tropical Depression 18 predicted to become Hurricane Rafael in the Caribbean » Yale Climate Connections

Hurricane Warning flags are flying in the Cayman Islands and a Hurricane Watch is up for western Cuba for Tropical Depression 18, which formed at 10 a.m. EST Monday over the warm waters of the Western Caribbean. TD 18 is expected to intensify into Tropical Storm Rafael by Monday evening, then affect Cuba as a Cat 1 hurricane on Wednesday morning.

TD 18 in the organizing phase

At 10 a.m. EST Monday, November 4, TD 18 was located 400 miles (645 km) southeast of Grand Cayman, headed north at 6 mph (15 km/h) with top sustained winds of 35 mph (55 km/h) and a central pressure of 1,003 mb. Satellite images showed that TD 18 was not yet well organized, with a modest amount of heavy thunderstorms that were steadily growing more organized. Conditions were very favorable for development, with light wind shear of 5-10 knots, a very moist atmosphere, and very warm ocean waters of 30 degrees Celsius (86°F) – about 0.5 to 2 degrees Celsius (1-2°F) warmer than average for early November.

PTC 18 has become TD18 after a well-defined center of circulation was confirmed by Air Force Hurricane Hunters @53rdWRS. Here’s a satellite loop of TD 18 showing the circulation tightening up south of Jamaica. No changes to track/intensity at this time. #FLKeys #FLwx #FloridaKeys pic.twitter.com/q2Xxts8Blu

— NWS Key West (@NWSKeyWest) November 4, 2024

Forecast for TD 18 in the Western Caribbean

A ridge of high pressure to the northeast of TD 18 will keep the storm moving on a mostly northwesterly track through Thursday, taking the center of the storm about 50-80 miles (80-130 km) west of Jamaica late Tuesday morning, through the Cayman Islands by Tuesday evening, then into western Cuba on Wednesday morning. Very favorable conditions for development are expected during this period, with light wind shear, warm waters with high heat content, and a very moist atmosphere. This will likely result in steady to rapid intensification (unless TD 18 passes close enough to Jamaica for significant land interaction to occur). The 6Z Monday runs of the HWRF, HMON, and HAFS-A dynamical hurricane models predicted that TD 18 would be a borderline tropical storm/Cat 1 hurricane on Wednesday morning when it is expected to make landfall in western Cuba. The HAFS-B model was more aggressive, predicting a Cat 3 landfall in Cuba. The 12Z Monday SHIPS model gave a 34% chance that TD 18 would intensify to a Cat 2 with 110 mph winds by Thursday morning, when the storm would be in the southeastern Gulf of Mexico.

TD 18’s impact on Cuba

TD 18 is expected to make landfall in Cuba at an inopportune time, as the island’s electrical grid is suffering continued instability after a nationwide blackout on October 18-21 caused by the failure of the Antonio Guiteras power plant, Cuba’s largest. This plant, located about 60 miles (95 km) east of Havana, is likely to be about 100 miles to the east of where the core of TD 18 passes, so may avoid significant impacts from the storm. Nevertheless, Cuba’s electrical infrastructure is so weak that the large number of power outages likely to occur in western Cuba may have an extended duration, and the nation’s entire grid may be at risk of collapse.  

More hostile conditions in the northern Gulf of Mexico

Passage over western Cuba is likely to disrupt TD 18, but once the storm emerges into the Gulf of Mexico, it is expected to move to the northwest over a tongue of warm waters of 27-28 degrees Celsius (81-82°F) associated with the Loop Current, which extends northward from the Western Caribbean into the central Gulf of Mexico. All four of the high-resolution dynamical hurricane models make TD 18 at least a Cat 2 in the central Gulf by Thursday. Just how intense TD 18 get will help determine where the storm goes, and this uncertainty is part of why the National Hurricane Center commented in its 10 a.m. EST discussion that the track forecast for TD 18 over the Gulf has higher uncertainty than usual. The GFS model and its ensemble members predict a continued northwesterly motion for TD 18, with a landfall near Louisiana late in the week. The UKMET model and the European model and its ensembles argue for a westward turn in the Gulf, well south of the northern Gulf Coast (see Tweet below).

The farther north in the Gulf of Mexico that Rafael progresses, the more hostile conditions for development will get. Recurring fall cold fronts have spread cool air over the Gulf in recent weeks, causing significant cooling of the waters. The waters within about 200 miles (320 km) of the northern Gulf of Mexico coast have chilled down to below 26 degrees Celsius (79°F). More importantly, the jet stream has shifted more to the south in recent weeks, and thus TD 18 will encounter high wind shear of 20-30 knots as it approaches the U.S. coast. In addition, very dry air with a midlevel relative humidity of 40-45% is expected over the northern Gulf late this week.

The combination of high wind shear, dry air, and cooler ocean temperatures will likely cause steady to rapid weakening, and none of the top intensity models show TD 18 hitting the U.S. as a hurricane. The main concern would be the potential for areas of heavy rain over the Southeast U.S., assuming that TD 18 were to track into the central Gulf Coast: The storm is predicted to be hauling unusually large amounts of atmospheric moisture for early November. It’ll be later this week before more clarity emerges on where and how much it might rain.

Another disturbance could approach the Bahamas and South Florida toward the coming weekend

The tail end of a Northwest Atlantic cold front may attempt to organize late this week into a tropical disturbance that will move west-northwest toward the Bahamas and South Florida. A few members of the European and GFS model ensembles show modest development of this disturbance as it moves around the south side of the unusually strong upper high over the Southeast U.S. and Northwest Atlantic that will also be steering Rafael. There is relatively high confidence in the steering pattern, and sea surface temperatures remain unusually warm — more than adequate to support a tropical cyclone. However, wind shear and the upper-level wind structure will be less than ideal, and the ensemble models strongly agree that only modest development is likely, perhaps prolonging a spell of gusty winds and rough marine conditions that will plague the region as TD 18 passes well to the west in the Gulf of Mexico.

In its Tropical Weather Outlook at 7 a.m. EDT Monday, the National Hurricane Center gave this future system a 20% chance of developing into at least a tropical depression in the seven-day period, with near-zero odds in the two-day window.

Patty goes from subtropical storm to tropical storm to remnant low in less than a day

Far away from the tropics, a broad area of low pressure behind a Northeast Atlantic cold front gathered enough showers and thunderstorms to become Subtropical Storm Patty early Saturday. With top winds that peaked at 65 mph, Patty passed through the Azores early Sunday without major impact, then briefly acquired just enough deep circulation, symmetry, and concentrated convection to become Tropical Storm Patty at 10 p.m. EDT Sunday. But increasingly cool water and increasing wind shear quickly took their toll, and at 10 a.m. EDT Monday, the National Hurricane Center reclassified Patty as a remnant low.

Patty’s remnants will arc poleward near the western Iberian Peninsula on Tuesday, perhaps bringing one to three inches of rain along and near the coast of Portugal and northwest Spain. Fortunately, the rains are expected to remain well away from the flood-ravaged areas of Valencia in eastern Spain.