Hurricane warning flags are flying in the Cayman Islands and western Cuba is under a hurricane warning due to Tropical Depression 18, which formed over the warm waters of the western Caribbean at 10 a.m. EST Monday. TD 18 is expected to develop into Tropical Storm Rafael on Monday evening and then hit Cuba as a Category 1 hurricane on Wednesday morning.

TD 18 in the organization phase

As of 10 a.m. EST on Monday, November 4, TD 18 was located 400 miles (645 km) southeast of Grand Cayman and moving north at 6 mph (15 km/h), with peak 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 number of severe thunderstorms that were steadily becoming more organized. Conditions were very favorable for development: light wind shear of 5-10 knots, a very humid atmosphere and very warm sea water of 30 degrees Celsius (86°F) – about 0.5 to 2 degrees Celsius (1-2°F) . warmer than average for early November.

PTC 18 became TD18 after a clearly defined orbiting center was confirmed by Air Force Hurricane Hunters @53rdWRS. Here is a satellite loop of TD 18 showing the circulation strengthening south of Jamaica. There are currently no changes to the route/intensity. #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 northeast of TD 18 will keep the storm on a predominantly northwesterly track through Thursday, passing through the center of the storm about 50-80 miles (80-130 km) west of Jamaica late Tuesday morning, crossing the Cayman Islands through Tuesday evening, then western Cuba on Wednesday morning . During this period, very favorable development conditions are expected with light wind shear, warm water with high heat content and a very humid atmosphere. This will likely result in steady to rapid intensification (unless TD 18 passes close enough to Jamaica to cause significant land interactions). The 6Z Monday runs of the HWRF, HMON and HAFS-A dynamic hurricane models predicted TD 18 would be a marginal tropical storm/Category 1 hurricane by Wednesday morning when it is expected to make landfall in western Cuba. The HAFS-B model was more aggressive and predicted a Category 3 landing in Cuba. The 12Z Monday SHIPS model showed a 34 percent chance that TD 18 would strengthen to Category 2 strength with winds of 110 mph by Thursday morning as the storm hits the southeastern Gulf of Mexico.

The impact of TD 18 on Cuba

TD 18 is expected to make landfall in Cuba at an inopportune time as the island’s power grid continues to fail following a nationwide blackout from October 18 to 21 caused by the failure of the Antonio Guiteras Power Plant, Cuba’s largest power plant instability suffers. This facility is located about 60 miles (95 km) east of Havana and is expected to be about 100 miles east of where the core of TD 18 passes, avoiding significant impacts from the storm. Still, Cuba’s electrical infrastructure is so weak that the large number of power outages likely to occur in western Cuba could be prolonged and the country’s entire power grid could be at risk of collapse.

More hostile conditions in the northern Gulf of Mexico

Passage over western Cuba is expected to disrupt TD 18, but once the storm reaches the Gulf of Mexico, it is expected to move northwestward over an associated tongue of warm waters of 27 to 28 degrees Celsius (81 to 82 °F). the Loop Current, which extends from the western Caribbean north to the central Gulf of Mexico. All four high-resolution dynamic hurricane models make TD 18 at least Category 2 in the central Gulf by Thursday. How intense TD 18 becomes will help determine where the storm goes, and that uncertainty is one of the reasons the National Hurricane Center in in his discussion at 10 a.m. EST noted that the trajectory forecast for TD 18 over the Gulf was subject to greater uncertainty than usual. The GFS model and its ensemble members predict continued northwestward motion for TD 18, with landfall near Louisiana late in the week. The UKMET model and the European model and their ensembles suggest a westward turn in the Gulf, well south of the northern Gulf Coast (see tweet below).

The further north in the Gulf of Mexico Rafael moves, the more adverse the conditions for development become. Recurring fall cold fronts have spread cool air across the Gulf in recent weeks, causing the water to cool significantly. Waters within about 200 miles (320 km) of the northern coast of the Gulf of Mexico have cooled to below 26 degrees Celsius (79°F). More importantly, the jet stream has shifted more southward in recent weeks and TD 18 will therefore experience strong wind shear of 20 to 30 knots as it approaches the US coast. Additionally, very dry air is expected over the northern Gulf late this week with a mean relative humidity of 40-45%.

The combination of strong wind shear, dry air, and cooler ocean temperatures will likely result in steady to rapid weakening, and none of the highest intensity models show TD 18 hitting the U.S. as a hurricane. The primary concern would be the potential for areas of heavy rain over the southeastern U.S. assuming TD 18 makes its way to the central Gulf Coast: The storm is expected to bring unusually large amounts of humidity in early November. It will be later this week before more clarity emerges about where and how much rain could occur.

There could be further unrest in the Bahamas and South Florida next weekend

The tail of a cold front in the northwest Atlantic may attempt to form into a tropical disturbance later this week, moving west-northwest toward the Bahamas and southern Florida. Some members of the European and GFS model ensembles show modest evolution of this disturbance as it moves around the southern side of the unusually strong upper high over the southeastern US and northwest Atlantic, which will also control Rafael. There is relatively high confidence in the steering pattern and sea surface temperatures remain unusually warm – more than sufficient to support a tropical cyclone. However, wind shear and upper-level wind structure will not be ideal, and ensemble models are in full agreement that only moderate development is likely, potentially extending a period of gusty winds and rough sea conditions that will affect the region as it passes by TD 18 will strike far 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 percent chance of developing into at least a tropical depression within seven days, with a near-zero chance in the two-day window .

Patty transitions from a subtropical storm to a tropical storm in less than a day and reaches its remnant low

Far from the tropics, a widespread low-pressure area behind a cold front in the northeast Atlantic gathered enough showers and thunderstorms to develop into subtropical Storm Patty early Saturday. With peak winds peaking at 65 mph, Patty crossed the Azores early Sunday without major impacts and then briefly gained just enough deep circulation, symmetry, and concentrated convection to become Tropical Storm Patty by 10 p.m. EDT Sunday. But increasingly cool waters and increasing wind shear quickly took their toll, and by 10 a.m. EDT Monday, the National Hurricane Center reclassified Patty as a remnant low.

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