Updated Saturday, 10 a.m. ET

Tropical Storm Melissa is organizing while it sits over the Caribbean southeast of Jamaica. The hostile upper-level winds that have been holding it back have let up enough that a partial eyewall has formed. Melissa will likely intensify into a hurricane in a matter of hours. Once the storm has its structure in place, rapid intensification is forecast over the near-record warm water.

If Melissa goes down the middle of the National Hurricane Center cone and intensifies as forecast, catastrophic damage is likely in Jamaica from feet of torrential rain and Category 4 or 5 winds. The assault will last more than two days – which is hard to imagine.

Landfall is still about 2 1/2 days away – so the forecast track can still shift, of course. But any reasonable alternate path would still produce a foot and a half to 3 feet of rain across the eastern two-thirds of the island. No place can handle that kind of rain, and when it’s an island with mountains that drain through towns and cities, the potential for widespread catastrophic flooding and mudslides is extreme. Here is the NOAA estimate for total rainfall through Tuesday from Melissa.

There is general agreement on the predicted track among the computer forecast models. Here are the official NHC forecast in red, the European (ENS) in yellow, and the Google DeepMind AI-based forecast in blue. All forecast an extreme threat to the eastern half of the island.

The yellowish and reddish areas show the forecast diameter of the winds of various strengths at 2 a.m. on Tuesday. Notice that the hurricane-force winds are forecast to be over the Kingston metropolitan area at that time.

South of Jamaica, the Caribbean water is extraordinarily warm, and the atmospheric pattern is forecast to be conducive to dramatic, rapid strengthening of the system. The National Hurricane Center is forecasting Melissa to reach high-end Category 4 or Category 5 strength before it turns north. The current consensus track shows an extreme threat to the Kingston metropolitan area from flooding rain, wind, and storm surge.

Kingston Harbor opens to the south, and the airport is on a peninsula in the harbor. Storm surge up to 10 feet above normal high tide is forecast for somewhere on the southern coast of Jamaica east of where the center comes ashore. If that occurs in Kingston or just west of the city, there will be widespread damage to critical infrastructure.

It’s too early to know exactly where the worst of the wind will be because it will occur in a relatively narrow corridor from south to north across the island. But the threat of extreme rainfall and widespread damage from floods and mudslides is likely to occur over a wide area.

The modern storm of record in Jamaica is Hurricane Gilbert from 1988. Gilbert caused devastation east to west, from one end of the country to the other. Melissa’s winds are forecast to be stronger than Gilbert’s, but the storm will be moving south to north. Damaging winds will not impact the entire island. Gilbert dumped almost 3 feet of rain in the mountains, which is similar to the estimates of the rainfall predicted from Hurricane Melissa.

Haiti and the Dominican Republic

Extreme rainfall is also forecast over the Tiburon Peninsula in southwest Haiti, with heavy rain in other parts of the country as well. Significant flooding has already occurred along the south coast of the Dominican Republic, including in Santo Domingo. Additional rainfall is expected.

Other Than Jamaica

Melissa will likely be weakened by its trek over the high terrain on Jamaica, but will still be a formidable storm when it makes landfall late Tuesday or early Wednesday in eastern Cuba. Mountains there and increasingly hostile upper winds should weaken it some as it moves through the southeastern Bahamas. The Turks and Caicos will also be impacted if Melissa takes the forecast track.

The Cayman Islands look to be outside of the extreme threat zone, although fringe effects are possible, especially in the waters around the islands.

Puerto Rico is on the edge of the moisture feed. Spotty tropical downpours could still occur until the storm moves west.

Everybody in the affected areas should put maximum effort into finding a safe place where the floods can’t reach them. People in areas near the storm’s track should be sure they are in a sturdy concrete building where they can hide from the wind.