Melissa simmers in the Caribbean, posing a serious flood threat and a track that’s hard to pin down

By CNN Meteorologists Briana Waxman, Mary Gilbert, CNN

(CNN) — Tropical Storm Melissa is crawling through the Caribbean Sea, threatening to unleash life-threatening flooding and mudslides across parts of the region later this week. It’s proof this year’s Atlantic hurricane season is not over yet, and Melissa has plenty of time and fuel ahead.

Melissa was about 300 miles south of Haiti with maximum sustained winds of 50 mph as of Wednesday morning, according to the National Hurricane Center. It was churning forward at an agonizingly slow 2 mph.

Heavy rain is already spreading north Wednesday as Melissa moves at a snail’s pace toward Jamaica and Haiti. A foot or more of rain is possible in southern parts of Haiti and the Dominican Republic through this weekend. That much rain over mountainous terrain in the area could trigger catastrophic flash flooding and landslides.

Melissa is moving over water that’s so warm it’s essentially rocket fuel for storms this late in the season, and is expected to hit hurricane status by Saturday morning.

When that happens, it will be the 2025 Atlantic season’s fifth hurricane and the first to spin up inside the Caribbean. It’s also increasingly likely Melissa could become the season’s fourth major hurricane — Category 3 or greater.

A hurricane watch has been issued for parts of Haiti and a tropical storm watch is in effect for Jamaica. There’s a low, but non-zero chance Melissa directly impacts the mainland United States, though details are still coming into focus.

Here’s what we know so far.

Two possible outcomes, neither good

Melissa’s exact track is still tricky to pin down, but there are two main scenarios. The possibilities have changed slightly from initial forecasts, but both place Hispaniola and Jamaica in harm’s way.

Melissa could bring more than a foot of rain to parts of Hispaniola, which is the island that houses the Dominican Republic and Haiti, as it drifts closer to the island through the weekend.

It’s still unclear exactly what parts of Haiti and the Dominican Republic would be subject to the heaviest rain, but the combination of torrential rain and mountainous terrain is a recipe for dangerous flash flooding and mudslides. Jamaica could also receive torrential, flooding rainfall beginning later this week.

The islands will also face strong, potentially damaging winds from Melissa, especially after it reaches hurricane strength Saturday, according to the hurricane center’s forecast.

Slow-moving storms like Melissa hit the same areas with torrential rain and strong winds for days, significantly increasing rainfall totals and the likelihood of power outages. Melissa will start moving quicker at some point, and exactly when and where that happens is extremely important to determine its impacts. It’s also still quite unclear.

If Melissa’s current forecast track holds and the storm moves slowly west toward an area south of Jamaica into early next week, it could end up where the atmosphere and extremely warm water align to boost the storm.

Melissa is now expected to become at least a Category 3 major hurricane by Monday morning.

Its anticipated explosion in strength from tapping into that energy is something that’s happening more often as the world warms due to fossil fuel pollution. Just this year, three of the four Atlantic hurricanes to date underwent extreme rapid intensification: Erin, Gabrielle and Humberto.

A stronger Melissa would eventually turn northeast next week and threaten other portions of the Caribbean, like Cuba. That scenario would increase the intensity of all of Melissa’s impacts from rain to wind and dangerous seas.

Alternatively, there’s still a chance that another weather pattern could pull Melissa north toward Jamaica or Haiti early next week. This path would likely prevent Melissa from reaching the strength it might in the first scenario, but could also mean a direct landfall and more concentrated impacts in either location.

Is this a threat to the US?

A direct hit on the mainland US is unlikely, but not impossible. At this time, the storm’s most likely impact to the US could be some rough surf and rip currents along the East Coast next week.

Florida could be in play if Melissa takes a turn to the north later than currently expected. In that case, Cuba and parts of the Bahamas could also be hit with Melissa’s wind and rain.

The odds of a hurricane landfall in the US really dwindle at the end of October and into November, but there have been notable late-season exceptions. Most recently, Hurricane Nicole slammed into Florida as a Category 1 in early November 2022 and Hurricane Zeta smashed into Louisiana as a Category 3 in late October 2020.

As Melissa continues to develop in the coming days, its track, strength and threats will come into sharper focus.

Atlantic hurricane season officially ends on November 30, though tropical systems can still form after that date.

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CNN Meteorologist Chris Dolce contributed to this report.