A sprawling, fast-moving tropical disturbance raced through the Windward Islands on Sunday and entered the Caribbean, where it’s set to become a formidable rainmaker for days on end. Odds are rising that Invest 98L will become a tropical storm later this week, and hurricane strength can’t be ruled out, especially if the system stalls over the exceptionally warm waters of the central Caribbean.
Even if 98L remains offshore, people along the south coasts of the Greater Antilles, especially the Dominican Republic, would be wise to prepare for the potential of torrential rains and flooding later this week on the north flank of 98L. Northern portions of Honduras and Nicaragua in Central America may also be at risk. Because of high wind shear from the placement of the subtropical jet stream from Florida eastward through the Bahamas, 98L is not expected to be a threat to the continental U.S. for at least the next week.
In its Tropical Weather outlook issued at 8 a.m. EDT Monday, the National Hurricane Center gave 98L a 50% chance of becoming at least a tropical depression by Wednesday (those odds were up from 30% odds in the Sunday evening advisory) and an 80% chance over the next week. The next name on the Atlantic list is Melissa.
Lots of questions over 98L’s track – but high confidence it’ll be a big rainmaker
98L swept across the Windward Islands as an open tropical wave, meaning it lacked the closed surface circulation needed to define it as a tropical cyclone. Winds gusted as high as 45 mph (74 km/h) on Sunday at the Grantley Adams International Airport in Barbados during heavy squalls as 98L passed. Other peak gusts included 32 mph (52 km/h) at St. Lucia and 37 mph (61 km/h) at Martinique.
By midday Monday, 98L was moving west at a brisk 15 to 20 mph (24-32 km/h) and was already approaching the central Caribbean. The system is likely to bring heavy rains to the ABC islands and along the northern coast of South America through Wednesday.
The rapid motion of 98L is expected to slow by Tuesday, when it may become clearer which of two starkly different model solutions is more likely to prove correct. For much of the weekend, the GFS model insisted that 98L will turn sharply northward by Wednesday, moving north-northeast over or near the Dominican Republic before heading into the open Atlantic. Meanwhile, the European model has favored a continued westward drift through the week. That model also projects an eventual north-northeast swing similar to the GFS, but one that’s farther west and doesn’t occur until at least the weekend or perhaps early next week, when a large trough is projected to form over the eastern United States. Under this scenario, 98L could affect Honduras, Jamaica, Cuba, and the Bahamas on its recurving path. Ensemble members from the Google DeepMind model, which has performed admirably well this hurricane season, include both the faster- and slower-turn possibilities.
High wind shear has been impeding 98L’s development thus far, but that shear is predicted to abate by midweek, bringing very favorable conditions for 98L to develop. Midlevel relative humidity, already around 70%, could get as high as 80% by Wednesday, providing an environment of unusually rich moisture for 98L to build its shield of showers and thunderstorms (convection). Sea surface temperatures over the central Caribbean are near 30.5 degrees Celsius (87°F) — the warmest on record by far for late October outside of 2023 and 2024. In addition, there is ample deep-ocean heat content. Such deep oceanic heat can keep a slow-moving tropical system from stirring up cold water that would otherwise hinder its growth.
How the outcomes would differ for the faster- and slower-turn scenarios
Faster: If 98L makes its northward turn on the earlier side, as in the GFS scenario, it will not have much time to organize and intensify into a strong tropical storm or hurricane. However, it would not necessarily be moving north at a rapid clip, and immense amounts of rain could fall along its track. Under this scenario, 98L would appear most likely to affect the Dominican Republic late this week. If this came to pass, rainfall totals of 5 to 10 inches (125-250 mm) could be widespread, perhaps including parts of Haiti and Puerto Rico, and a narrow corridor of much larger amounts along 98L’s immediate path could exceed 20 inches (500 mm). Such rains could be expected to produce significant flash flooding and mudslides.
Slower: Should 98L linger over the central Caribbean later this week, significant strengthening into a tropical storm or hurricane will become more likely. Strong westerly winds are expected to keep 98L from advancing northwest into the Gulf of Mexico, but Honduras, Nicaragua, Jamaica, Cuba, and the Bahamas could be at risk if 98L waits to make its expected northward turn until the weekend or early next week.
When will we know more? It will likely take until 98L forms a closed low-level circulation – perhaps Tuesday, but possibly Wednesday or even later – before there is more consistency among top longer-range models on its future strength and motion. Likewise, short-range hurricane intensity models are much less reliable and consistent until a low-level center has formed.
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