Tropical Storm Isaias Sputtering in Bahamas, Will Approach Florida Tonight, Then Race Up East Coast

Winds have decreased slightly in Isaias as the storm fights with dry air and wind shear, and tries to recover from interaction with the Bahamas' Andros Island.

Watches, Warnings and Current Conditions

A hurricane warning is in effect from Boca Raton to the Flagler/Volusia County Line in Florida. A hurricane warning means that hurricane conditions are expected within the warning area within 36 hours.

(MORE: Hurricane Season Terms You Need to Know)

Hurricane warnings continue in the Northwest Bahamas, including Nassau, Freeport and the Abacos Islands.

Tropical storm warnings are in effect from the northern Florida Keys to Boca Raton and inland/north to Orlando, Florida, including Lake Okeechobee. They also extend from the Volusia-Flagler County line to Ponte Vedra Beach, Florida.

A tropical storm watch has been extended northward to the South Santee River in South Carolina, and continues to stretch southward to Ponte Vedra Beach, Florida.

In addition, a storm surge watch has been issued from Jupiter Inlet to Ponte Vedra Beach. This means that there is a possibility of life-threatening inundation from rising water moving inland during the next 48 hours.

The center of Isaias moved over northern Andros Island in the Northwest Bahamas, Saturday afternoon, where a gust to 69 mph was measured by a U.S. Navy site. The remnants of an eyewall are now moving northwestward from Andros Island and Paradise, according to the Bahamas radar.

Strong winds are moving through South Florida with the first band of rain from Isaias. Sites across coastal South Florida have reported wind gust in the 40-60 mph range, including a report of a 59 mph wind gust near Dania Beach, Florida.

Heavy rain and strong winds are pulling away from New Providence Island, including the Bahamian capital, Nassau. A wind gust to 50 mph was clocked at Nassau International Airport, and power was shut off to some parts of the island as a precaution.

(LATEST NEWS: Isaias Impacts in the Bahamas)

Latest Forecast

Here is our latest forecast path, from the National Hurricane Center.

There are still some important uncertainties.

First, Isaias is struggling mightily against the twin nemeses of dry air and wind shear, the change in wind speed and/or direction with height, despite plentiful warm water in its path.

The NOAA Hurricane Hunters found desert air is lurking west and southwest of Isaias' eyewall, Saturday morning. Strong winds aloft are from the southwest are blowing this dry air into Isaias' circulation, keeping it lopsided and could be weakening it.

We don't expect much of any significant strengthening, but it could regain hurricane status Saturday evening.

The next question, now, is how close Isaias' center comes to the Florida Atlantic coast Saturday night into Sunday night. The strongest winds typically occur in a band of convection near the center, known in a hurricane as an eyewall.

Residents of Florida will remember that the eyewall of much stronger and also larger Hurricane Matthew remained just offshore as it moved northward parallel to the Florida East Coast. Much of coastal east-central Florida received wind gusts of 60-80 mph, but Cape Canaveral, a section of land that juts out less than 15 miles into the Atlantic, received wind gusts well over 100 mph. These higher winds caused millions of dollars at NASA's Kennedy Space Center.

These kinds of winds are unlikely in Isaias, but the general idea remains: stronger winds could scrape along the coast.

This is the difference between being in the eyewall of a hurricane vs. just outside of the eyewall.

For now, we expect there's a good chance Isaias will pass close enough to scrape at least part of Florida's Atlantic coast where hurricane warnings are in effect.

After that, the forecast track is going to lean heavily on steering features in the atmosphere – the Bermuda high and an upper-level dip in the wind flow over the Mississippi Valley.

Isaias is expected to make a northward, then northeastward turn beginning Monday.

From there it could pass near the Carolinas Monday into Tuesday as a tropical storm , then sweep quickly near parts of the Northeast Seaboard as far north as New England Tuesday into Wednesday.

Potential Impacts

Wind

As mentioned earlier, Isaias is producing strong wind gusts and bands of heavy rain over the northern Bahamas and increasingly into South Florida.

Tropical storm conditions are expected by Saturday night in South Florida, then Sunday afternoon in central Florida.

Remember, winds will be strongest near the coast and in high rise buildings.

Here's what the wind field might look like early Sunday with the strongest gusts touching the coast of Florida.

Storm Surge

A dangerous storm surge is possible along Florida's East Coast and in the Bahamas.

A dangerous storm surge of up to 3 to 5 feet, above ground level, is forecast from the National Hurricane Center, in areas where winds will blow onshore in the Northwest Bahamas.

Storm surge watches have been issued from Jupiter Inlet to Ponte Vedra, Florida, where a storm surge of 2 to 4 feet, above ground level, is possible if peak surge occurs at the time of high tide. A storm surge of 1 to 3 feet may occur from North Miami Beach to Jupiter Inlet.

The high tides of most concern are Sunday morning in South Florida, and Sunday evening farther up the Florida coast.

Swells generated by Isaias are arriving along the Southeast coast of the U.S. leading to high surf and the danger of rip currents. Surf will remain elevated through the duration until Isaias passes.

Rainfall Flooding

It appears that Isaias could be eastward-loaded in terms of its precipitation patterns, meaning much of its rainfall could be over the Atlantic rather than over Florida. This pattern is expected to change as Isaias moves northward.

Rainfall of 4 to 8 inches is likely in parts of the Bahamas with up to 4 inches in portions of Cuba. Life-threatening flash flooding and mudslides are possible.

Two to four inches of rainfall is possible in east-central Florida through Monday, with isolated maximum totals of 6 inches, according to the National Hurricane Center.

Heavy rainfall may also spread into the Carolinas and mid-Atlantic later Monday into Wednesday.

For more on possible impacts in the mid-Atlantic and Northeast, read our latest discussion here.

Storm History

Isaias is the earliest named ninth Atlantic tropical cyclone on record. The previous record was Irene on Aug. 7, 2005.

Typically the ninth named tropical system occurs in the Atlantic basin in early October, meaning this year's pace is over two months ahead of average.

(MORE: The 2020 Atlantic Hurricane Season Is on a Record Pace)

Heavy rain triggered serious flash flooding in several areas of Puerto Rico. Just under 4.5 inches of rainfall was measured in San Juan on Thursday.

Multiple fallen trees, mudslides and flooding was reported in southwest Puerto Rico, according to local emergency management. River flooding has been recorded by USGS gauges in several locations in Puerto Rico.

(NEWS: Deadly Isaias Has Left Widespread Damage Across Dominican Republic, Puerto Rico)

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