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
611 Comments
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DEN
DEN
10 days ago

THE WORST PREDICTIONS AND FORCASTTING OF THIS STORM IN HISTORY….. NOTHING THEY SAID FOR 7 DAYS NOW HAS BEEN ACCURATE

DEN
DEN
11 days ago

ISASIS IS NOW TOAST…. AS I PREDICTED AND BEEN SAYING FROM LAST WEDNESDAY NIGHT

DEN
DEN
11 days ago

AS I HAVE BEEN SAYING FOR 3 DAYS AND GETTING LAUGHED AT MY PREDICTIONS THAT THIS STORM WILL DO NOTHING TO FLORIDA AND PROBABLY GO POOF …. AND I HAVE BEEN RIGHT ON… GET ME A JOB AT THE NHC WHO CANT EVER GET ANY FORCASTS CORRECT

DEN
DEN
11 days ago

AS OF 5AM THIS STORM IS TOAST

DEN
DEN
11 days ago

I am still saying that this storm will stay east off Florida and not make a landfall and Florida will not get to much from it

Bilge Rat
Bilge Rat
11 days ago

Track shifted West at 5:00PM, EST to include warnings for Rat’s Mouth and adjacent coastal locations. At 80mph max predicted windspeed this is a “patio furniture” threat to South Florida.

Bilge Rat
Bilge Rat
12 days ago

Why do they call it a cone? Beginning at a known position, the more the distance, the location of the center becomes less precise, so the forecast area becomes wider. This increased width at five days, three days, etc. may include areas that do not in fact sustain a direct hit from the center of the disturbance. There are variables that affect tracks known to the models that predict. While history of tracks is one variable, history alone does NOT accurate predictions make. “The last five missed me so the sixth will not”. Good luck with that.

DEN
DEN
12 days ago

JULY 21 8AM FROM THE NHC THE CONE SHIFTED A BIT MORE EAST AWAY FROM FLORIDA

DEN
DEN
12 days ago
Reply to  DEN

OOPS JULY 31ST

DEN
DEN
12 days ago

Why people are not on Yale Eye On The Storm blog?

DropDeadFred
DropDeadFred
12 days ago

BOOM! Here comes DOOM!

DEN
DEN
12 days ago

5 DAY OUT ITS A DIRECT FLORIDA HIT 2 DAYS OUT THIS IS WHAT FLORIDA GETS

listenerVT
listenerVT
13 days ago

Hurrah, we’re back!

Thank you Doc Masters and Bob!!

Hank
Hank
13 days ago

Test

gulfbeachgal
gulfbeachgal
13 days ago

test

Lenore F Taylor
Lenore F Taylor
13 days ago

test

Bilge Rat
Bilge Rat
13 days ago

The science of unsupported assumptions Is something to behold, just not something to base either decisions or actions upon. Florida does not have a good track record in this regard, these days.

DEN
DEN
13 days ago

this storm will not effect florida at all… its the same shift east shift east every year after they have it directly slamming florida 5 days out……

DEN
DEN
13 days ago

like i have been saying for days now… when they have florida in the middle of the cone with a direct hit at 5 to 6 days out by 3 days out florida is spared again… this storm will keep tracking east and not give florida anything to speak of….. THE usual huge hype for florida

Dobby
Dobby
13 days ago
Reply to  DEN

Well, you certainly said it four times in a row just now … 😀

DEN
DEN
13 days ago
Reply to  Dobby

AND AS OF THE NEW 5PM TRACK I AM RIGHT IT MISSES FLORIDA AGAIN WITH THE BIG HOOK

Dobby
Dobby
12 days ago
Reply to  DEN

So, five times now …

DEN
DEN
13 days ago

not gonna touch florida at all …. the mystery trough has suddenly appeared as usual to save florida…. once again all the hype and this storm will curve ots just wait and see

DEN
DEN
13 days ago

BY 11am the track will move further east and by 5 pm tonight even further eas\t and as usual florida was in the center of the track at 5 days out and by 2 to 3 days out it misses florida….. see it every year

Deb Frisco
Deb Frisco
13 days ago

Glad to have a new blog site!

Knock on Wood
Knock on Wood
13 days ago

Thank you Skye for the temporary home while waiting for this. Your site really is great

Hurricane Watcher61
Hurricane Watcher61
13 days ago

Test Test

Raymond Oliva
Raymond Oliva
13 days ago

Test

MissyGal
MissyGal
13 days ago

Testing 1,2