FORT LAUDERDALE, FLA.—The threat of tropical storm or hurricane conditions impacting Florida from Dorian has increased, the National Hurricane Center said in its 5 p.m. EDT update Tuesday.

“Residents in these areas should monitor the progress of Dorian and ensure that they have their hurricane plan in place,” the hurricane centre said.

So far on Tuesday the official hurricane centre forecast was continuing to show Dorian either remaining as a tropical storm or edging very close to hurricane status — instead of becoming an all-out hurricane — by the time the storm starts knocking on Florida’s door.

That’s because there is a disparity in the various forecasting computer models monitored by hurricane experts. While some are showing Dorian intensifying, others suggest the storm will not —contributing to a lack of confidence so far when it comes to predicting how strong the storm will be by Saturday when it’s expected to reach the Sunshine State.

“Wind and rain impacts from Dorian are possible in South Florida later this week and this weekend,” said Robert Molleda of the National Weather Service’s Miami-South Florida forecast branch, in a statement Tuesday afternoon.

“The high amount of uncertainty in the storm’s intensity and exact track over the Bahamas means that we can’t pinpoint potential landfall points or specific impacts at this time. Continue monitoring the progress of Dorian over the coming days.”

A forecast discussion, basically a technical analysis for meteorologists, posted on the National Hurricane Center’s website at 11 a.m. on Tuesday explains that “the models continue to indicate that the upper-level flow pattern and shear conditions are expected to remain favorable for strengthening throughout the forecast period, so it is uncertain why the dynamical models are not showing more development and strengthening.”

The major make-or-break point in Dorian’s path that is also contributing to the uncertainty is how the storm will interact with Hispaniola, basically the land mass that includes the Dominican Republic and Haiti, and Puerto Rico. Whether these islands and their mountains will weaken Dorian remains to be seen.

Bottom line: Nobody really knows with much certainty how strong the storm will be by the time it potentially approaches Florida.

“Given the large spread in the guidance, there is lower than normal confidence in the intensity forecast, especially on days 4 and 5,” the forecast discussion says.

On Tuesday, Tropical Storm Dorian was bringing heavy rains and gusty winds to the eastern Caribbean as it moved over the islands that form the eastern gateway to the Caribbean.

At 5 p.m. Tuesday, the centre of Dorian was located about 130 kilometres west of Dominica with maximum sustained winds of 80 kph and moving toward the northwest at 21 kph, according to the National Hurricane Center.

After entering the Caribbean Sea, Dorian could strengthen to a hurricane before it reaches Puerto Rico on Wednesday and the Dominican Republic later Wednesday and Thursday.

As a result a hurricane watch was in effect for Puerto Rico and parts of the Dominican Republic. A hurricane watch means hurricane conditions are possible within the next 48 hours.

Puerto Rico is still recovering from the devastation of 2017’s Hurricane Maria.

By Thursday night and Friday, Dorian will be closing in on the southeastern Bahamas. So far Dorian was expected to be a tropical storm as it reaches the Bahamas.

The director of the National Hurricane Center, Kenneth Graham, said Tuesday in an interview on WSVN-TV that there are so many unknowns that it’s hard to predict Dorian’s impacts on South Florida.

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“It’s such an undetermined situation here. If it’s a weaker storm you can see some gusty winds and some rainfall but if it stays stronger — right now we’re looking at the potential for a tropical storm,” he told the station.

“So, preparedness is everything, it’s having that plan ready just in case,” Graham said.

Because of the tropical storm, Miami-based Royal Caribbean rerouted its Symphony of the Seas, Allure of the Seas and Harmony of the Seas ships from eastern to western Caribbean routes. “We continue to monitor the path of Tropical Storm Dorian and potential impact to our vessels and will communicate any scheduling changes to our guests,” spokeswoman Melissa Charbonneau said.

Carnival Cruise line, based in Doral, issued a statement saying it, too, was monitoring Dorian. “The safety of our guests and crew is our No. 1 priority and our ships will remain a safe distance from the storm at all times. In the event any changes to our itineraries are necessary, we will update our guests accordingly.”

Carnival said all of its ships that call on ports in the Caribbean and the Bahamas were avoiding the storm.

Dorian is a relatively small storm physically with tropical storm-strength winds extending up to 72 kilometres out from the core. The storm’s winds, at 80 kph, did not change during the overnight hours.

Hurricanes are marked by a minimum top wind strength of 119 kph.

The storm is expected to strike or pass very close to the Dominican Republic with winds at or near 113 kph, according to the National Hurricane Center.

Meanwhile, Tropical Depression Six formed about 587 kilometres southeast of Cape Hatteras, N.C., on Monday but was far enough out in the water to pose no threat to the United States.

Hurricane season runs from June 1 to Nov. 30, but 95 per cent of storms are produced during the peak period from mid-August to late October, and the National Oceanic and Atmospheric Administration has warned that conditions could be favourable for more dangerous storms than initially projected.