PTC9
Infrared satellite image of Potential Tropical Cyclone Nine (PTC 9) approaching the Lesser Antilles Islands at 11 a.m. EDT Tuesday, July 28, 2020. Superimposed in warm colors are the location of dust and dry air of the Saharan Air Layer (SAL), which lay just to the north of PTC 9. (Image credit: University of Wisconsin.

A large and vigorous tropical wave in the central tropical Atlantic, located about 300 miles east of the Leeward Islands, was designated Potential Tropical Cyclone Nine (PTC 9) by NOAA’s National Hurricane Center (NHC) at 11 a.m. EDT Tuesday, July 28.

PTC 9 had top sustained winds near 40 mph and was headed west at 23 mph. It is predicted to bring tropical storm conditions with heavy rains of 3 – 6 inches to the Leeward Islands, the Virgin Islands, and Puerto Rico on Wednesday. PTC 9’s winds are likely stronger than 40 mph, since an Air Force hurricane hunter aircraft investigating the storm Tuesday afternoon found winds of 60 – 65 mph at 10,000 feet in altitude, which typically implies surface winds near 55 mph.

PTC 9 had favorable conditions for development on Tuesday afternoon, with sea surface temperatures near 28 degrees Celsius (82°F) and moderate light shear of 5 – 10 knots. The system was embedded in a moderately dry atmosphere with a mid-level relative humidity of 60%. Satellite images on Tuesday showed that PTC 9 was large and elongated, with two areas of concentrated heavy thunderstorm activity, one to the west-southwest, and one to the east-northeast. The future track and intensity of PTC 9 will heavily depend upon which of these two areas PTC 9 ends up consolidating around. A more northerly location would likely lead to a stronger storm.

Satellite view
Figure 1. Visible GOES-17 satellite image of PTC 9 at 15:20Z (11:20 a.m. EDT) Tuesday, July 28, 2020. (Image credit: NOAA/RAMMB)

Forecast for PTC 9

As PTC 9 progresses mostly west-northwestward at 15 – 20 mph over the next few days, it will have to contend with dry air from the Saharan Air Layer, located to its north. The 12Z Tuesday run of the SHIPS model predicted that the atmosphere surrounding the system would slowly dry to a relative humidity of 55% by Thursday. However, the model predicted that wind shear would remain light to moderate, 5 – 15 knots, for the remainder of the week, making it feasible for PTC 9 to wall off the dry air to its north and form a strong inner core region of heavy thunderstorms resistant to the dry air.

SSTs will warm to 29 degrees Celsius (84°F) by Thursday, which will aid the intensification process. Also favoring intensification will be a large-scale region of ascending air over the Atlantic, caused by passage of an atmospheric disturbance called a Convectively Coupled Kelvin Wave (CCKW), as explained in a tweet by Michael Ventrice.

Steering currents will likely carry the system very close to Hispaniola on Thursday, and passage close to this mountainous island could significantly disrupt PTC 9’s circulation.

The 11 a.m. EDT Tuesday NHC intensity forecast called for PTC 9 to remain below hurricane strength, peaking with 60 mph winds this weekend. Several of the top intensity models also predicted that PTC 9 would not become a hurricane. However, some models are predicting PTC 9 will be a hurricane this weekend as it moves through the Bahamas and approaches the southeastern U.S. coast. The most startling prediction came from the 12Z Tuesday run of the SHIPS model, which gave a 55% chance that PTC would rapidly intensify by 75 mph in 72 hours. However, PTC 9 would have to get organized in a hurry, becoming a tropical storm on Tuesday, in order for the storm to intensify so quickly.

PHOTO Survivors of Hurricane Maria hand out fruit trees in Puerto Rico

The uncertainty in the future intensity of PTC 9 is very high, but it will be no surprise if it becomes a hurricane late this week.

The three best models for predicting tropical cyclone genesis – the European, GFS, and UKMET models – all support intensification of PTC 9 into a tropical storm by Thursday, July 30. In an 8 a.m. EDT Tuesday Tropical Weather Outlook, NHC gave PTC 9 two-day and five-day odds of formation of 80% and 90%, respectively.

The next name on the Atlantic list of storms is an obscure one, “Isaias” (pronounced ees-ah-EE-ahs). The earliest ninth storm in Atlantic tropical history was Irene on August 7, 2005; The earliest “H” storm prior to Hanna of this year was Harvey on August 3, 2005.

Topics: Weather Extremes
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DEN
DEN
3 days ago

ALOT OF TYPICAL HYPE AGAIN THIS YEAR … FLORIDA WONT GET ANYTHING THIS YEAR ANY STORMS THAT FORM WILL GO EVERYWHERE BUT FLORIDA

DEN
DEN
10 days ago

also since yesterday they have been saying that georgia an s. carolina will get hit hit from this storm and they wont get anything either… more retail scam

DEN
DEN
11 days ago

complete busted forcast here in daytona beach…… 21 different tracks and changes since thursday and all inaccurate

DEN
DEN
11 days ago

Ok here are the stats and why people in east central florida ignore the weather reports…. since 1987 there have been 46 out of 51 times that they predicted a hit with terrible weather from a tropical storm/ hurricane here and 46 times it was a bust just like this isaisis storm… its all about getting people to spend money at the weather channels main sponsors… walmat, home depot lowes etc etc …

DEN
DEN
11 days ago

no body here every believes what the nhc has to say… bussiness as usual

DEN
DEN
11 days ago

finally last night the nhc was positive this storm would come inland by volusia and brevard giving us very high winds and rain.. and yet another busted forcast

DEN
DEN
11 days ago

nhc is a laughing stock

DEN
DEN
11 days ago

had 20 times worse conditions last mon tues and wenesday with t storms

DEN
DEN
11 days ago

here in daytona beach they said 50 to 70mph winds and 3 – 5 inches of rain and its hot and sunny out……another typical bust forcast by the experts

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