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Tropical storm warnings issued for Puerto Rico, Virgin Islands with Isaias likely to form

This would be the earliest 'I' storm on record in the Atlantic

The tropical disturbance spins over the Atlantic on Tuesday. (RAMMB/CIRA)
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It may only be late July, but the Atlantic Ocean appears to be on the verge of cranking out its ninth named storm of the 2020 hurricane season, a milestone more typical of late September.

Meteorologists are watching an area of disturbed weather and swirling thunderstorms nearing the Lesser Antilles. It’s producing winds near tropical storm force, but it isn’t well organized with a clear center of circulation.

However, the National Hurricane Center anticipates this area of disturbed weather will become Tropical Storm Isaias before reaching Puerto Rico and the Leeward Islands on Wednesday through Thursday. The main impacts in these areas will be gusty winds and heavy rain as the system continues to develop.

As of Tuesday morning, the National Hurricane Center began issuing advisories on the nascent system as it gathered strength. An Air Force Reserve Hurricane Hunter mission into the disturbance is scheduled for Tuesday afternoon.

Tropical storm warnings are up for Puerto Rico, including Vieques and Culebra, as well as the U.S. Virgin Islands. Antigua, Barbuda, the British Virgin Islands, Guadeloupe, Martinique and St. Maarten are also under a tropical storm warning. Heavy rain totaling 3 to 6 inches, with localized 10-inch amounts, is possible across the northern Leeward Islands, Puerto Rico and surrounding areas, the NHC warns, yielding the potential for flash flooding.

The name Isaias is a Spanish version of the biblical name Isaiah, and is pronounced “ees-ah-EE-ahs.”

If it is named as expected, it would obliterate the record for the earliest “I” storm, currently held by Irene, which was named more than a week later, on Aug. 7, 2005.

The system eventually could affect the southeastern Lower 48 states, with Florida at particular risk.

The Atlantic hurricane season is off to a record fast start and is likely to get worse

This season has also featured the earliest “C,” “E,” “F,” “G,” and “H” storms on record — Cristobal, Edouard, Fay, Gonzalo and Hanna.

Hurricane season outlooks predicted that 2020 would yield an unusually active hurricane season, with above-average odds of a U.S. landfall. Anomalously warm ocean sea surface temperatures present in the tropical Atlantic, including off the East Coast and in the Gulf of Mexico, will exacerbate the threat, bolstering the potential intensity of cyclones that form.

The United States has already been hit by a hurricane this season, with Category 1 Hurricane Hanna striking Texas over the weekend.

Tracking the storm

On Tuesday morning, satellite imagery revealed the disturbance — dubbed Potential Tropical Cyclone 9, or PTC9 — swirling about 700 miles east of the Windward Islands. On satellite imagery, PTC9′s rotation appeared broad and elongated. Although the system has plenty of spin, or vorticity, it won’t be able to consolidate and intensify until that spin becomes more concentrated. That could inhibit its development somewhat.

Thunderstorm activity had dramatically increased in areal coverage and intensity late Monday into early Tuesday, though. That’s a sign that PTC9 is beginning to organize.

Buoy data supports the strengthening trends seen with PTC9. One buoy, located under the roiling mass of swirling clouds, reported winds gusting upward of 40 mph on Tuesday morning, with falling air pressure. Tropical storm force winds begin at 39 miles per hour.

The winds are near the 39 mph sustained threshold for a tropical storm, but whether one is named is predicated on those winds being coiled about a clearly defined center. That’s what the Hurricane Hunters will be in search of Tuesday afternoon.

Two factors that support intensification are warmer sea surface temperatures as the storm moves west-northwest, as well as less intrusion of dry air that had worked against the storm’s development on Sunday into Monday.

A tricky forecast

The disorganized nature of the storm makes predicting its intensity and track more difficult, because it can introduce errors in the initial conditions computer models base their projections on.

The National Hurricane Center noted that issue in a discussion Tuesday morning, writing: “It cannot be stressed enough that since the system is still in the formative stage, greater than average uncertainty exists regarding both the short-term and longer-term track and intensity forecasts.”

Depending on PTC9′s track, gusty winds and heavy downpours are possible in the Leeward Islands late Tuesday and Wednesday and Puerto Rico on Wednesday or Thursday. The rainfall is good news for Puerto Rico, which has suffered a severe drought recently.

After its potential encounters with Puerto Rico and Hispaniola, a sprawling high-pressure system over the Atlantic may force soon-to-be Isaias west-northwestward, bringing it precariously close to the Bahamas and the Southeastern United States this weekend.

The National Hurricane Center expects Isaias to remain at tropical storm intensity, due to strong upper-level winds that could limit its intensity, while it passes near or over several islands in the Bahamas before potentially making landfall in Florida over the weekend.

Hurricane season historically peaks in mid-September, so months of the season are left to go.