Tropical storm Isaias radar
Radar image of Tropical Storm Isaias at 11:14 a.m. EDT Thursday, July 30, 2020. Intense rainbands were affecting the island of Puerto Rico. (Image credit: National Weather Service via Mark Nissenbaum/Florida State University)

Tropical Storm Isaias (pronounced ees-ah-EE-ahs) formed on Wednesday night over the eastern Caribbean, bringing torrential rains and tropical storm-force winds to Puerto Rico and the Dominican Republic on Thursday. Isaias’s formation date of July 30 (Greenwich time) comes nearly a week earlier than the previous earliest appearance of the Atlantic’s ninth storm of the year, Irene, on August 5, 2005.

Tropical storm warnings and watches were in effect Thursday from Puerto Rico and the Virgin Islands into the Bahamas. A warning means tropical storm conditions are expected in the next 36 hours, and a watch means tropical storm conditions are possible within 48 hours. A tropical storm watch will likely be issued for portions of Florida later Thursday, since Isaias is likely to spread heavy rains into southeast Florida beginning on Saturday morning.

Figure 1
Figure 1. Visible GOES-17 satellite image of Isaias at 15:15Z (11:15 a.m. EDT) Thursday, July 30, 2020. (Image credit: Tropical Tidbits)

Long-range radar out of Puerto Rico on Thursday afternoon showed very heavy rainbands from Isaias were affecting Puerto Rico and the Dominican Republic. Numerous flash flood warnings and severe thunderstorm warnings were issued on Thursday for Puerto Rico. As of 9:30 a.m. EDT Thursday, the National Weather Service in San Juan, Puerto Rico, listed seven rivers on the island that were above flood stage, and 15 others near flood stage. Rainfall was heaviest on the western end of the island, with six Weather Underground personal weather stations reporting over 5 inches of rain. The peak rainfall amount was measured at Haciendas del Club on the west coast of the island, where 19.05″ had fallen as of 1:05 p.m. EDT Thursday.

At 11 a.m. EDT Thursday, Isaias was located near the southeastern coast of the Dominican Republic, with top sustained winds near 60 mph and a central pressure of 1003 mb. Punta Cana, on the eastern tip of the Dominican Republic, reported a wind gust of 60 mph late Thursday morning. Satellite images showed that Isaias was steadily growing more organized, with a large area of intense thunderstorms building near the surface circulation center, with additional low-level spiral bands forming. Isaias had favorable conditions for development, with sea surface temperatures (SSTs) near 29 degrees Celsius (84°F) and moderate wind shear of 10 – 15 knots. The system was embedded in a moderately dry atmosphere with a mid-level relative humidity of 60%, but the absence of strong wind shear to a large extent was allowing the storm to wall off the dry air of the Saharan Air Layer to its northwest.

Figure 2
Figure 2. Predicted surface wind (colors) and pressure (black lines) at 12Z (8 a.m. EDT) Saturday, August 1, 2020, from the 6Z Thursday, July 30, 2020 run of the HWRF model. The model predicted that Isaias would be passing through the northwestern Bahamas as a strong tropical storm with peak winds of 56 knots (64 mph, orange colors) and a central pressure of 991 mb. (Image credit: Tropical Tidbits)

Forecast for Isaias

Isaias will pass over Hispaniola on Thursday, and the mountainous terrain on the island will likely significantly disrupt Isaias’s circulation. The uncertainty in the future of the storm remains very high until it becomes apparent how the encounter with the island affects Isaias’s circulation and center location.

Isaias will also have to contend with dry air from the Saharan Air Layer, which surrounds it on three sides. The 12Z Thursday run of the SHIPS model predicted that the atmosphere surrounding Isaias would remain dry during the next five days, with a mid-level relative humidity of 50 – 55%. The model also predicted that wind shear would rise to a moderately high 15 – 25 knots on Friday through Monday, which should interfere with intensification by driving the dry air surrounding the storm into its core.

Figure 3
Figure 3. Infrared satellite image of Isaias at 8 a.m. EDT Thursday, July 30, 2020. Superimposed in warm colors are the location of dust and dry air of the Saharan Air Layer (SAL), which surrounded Isaias on three sides. (Image credit: University of Wisconsin)

However, SSTs for Isaias will warm to 30 degrees Celsius (86°F) by Saturday, 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.

The 11 a.m. EDT Thursday National Hurricane Center (NHC) intensity forecast called for Isaias to remain just below hurricane strength, peaking with 70 mph winds this weekend. Most of the top intensity models predicted that Isaias would peak as a strong tropical storm or low-end category 1 hurricane. A good uncertainty range for Isaias’s peak intensity this weekend off the Southeast U.S. coast is 60 – 85 mph, and I expect that we will see Isaias peak as a category 1 hurricane.

Figure 4
Figure 4. Visible satellite image of 93L at 11:05 a.m. EDT Thursday, July 30, 2020. (Image credit: Tropical Tidbits)

Invest 93L off the coast of Africa close to tropical depression status

A strong and well-organized tropical wave off the coast of Africa was designated Invest 93L by NHC on Thursday morning. A Thursday morning pass by the ASCAT satellite showed that 93L had a well-defined surface circulation, and satellite images revealed a well-organized system with plenty of heavy thunderstorms. In an 8 a.m. EDT Thursday Tropical Weather Outlook, NHC gave 93L two-day and five-day odds of formation of 20%. I think that these odds are too low, and should be 60%.

The system is expected to head north-northwest into a stable air mass and over cooler waters this weekend, and it likely will dissipate early next week.

The next name on the Atlantic list of storms is Josephine. The current record for earliest 10th Atlantic named storm formation is August 22, when Jose formed in 2005.

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Topics: Weather Extremes
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Skyepony (mod)
Skyepony (mod)
14 days ago
Gene
Gene
15 days ago

Test

hurricane_guineapig
hurricane_guineapig
15 days ago
Reply to  Gene

A+

Weatherman Will
Weatherman Will
15 days ago

B- at best 😉

MIAWeatherPilot
MIAWeatherPilot
15 days ago

Its a blog not a dissertation, hahahaha.

That Guy
That Guy
15 days ago

One day, we’ll all look back on summer of 2020, during pandemic, and remember when blog “made the switch,” and how crazy it all was, and how comments were barely working, and remember when we had to XYZ, etc.

Sort of like how our ancestors reminisced about having to not die by fighting large animals and spending entire sub-zero temp winters without clothes, etc.

bob therriault
bob therriault
15 days ago
Reply to  That Guy

Walking to school uphill, both ways!

Andre Brooks
Andre Brooks
15 days ago

ISAIAS BRINGING HEAVY RAINFALL AND TROPICAL-STORM-FORCE WINDS TO PORTIONS OF THE DOMINICAN REPUBLIC…
2:00 PM AST Thu Jul 30
Location: 18.9°N 69.8°W
Moving: NW at 20 mph
Min pressure: 1003 mb
Max sustained: 60 mph

hurricane_guineapig
hurricane_guineapig
15 days ago

test, I didn’t see my last post come up

isaias.jpg
hurricane_guineapig
hurricane_guineapig
15 days ago

And of course it starts working just as I’m flipping out xD

Patrap
15 days ago

comment image

Andre Brooks
Andre Brooks
15 days ago

026
NOUS42 KNHC 301730
REPRPD
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
0130 PM EDT THU 30 JULY 2020
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 31/1100Z TO 01/1100Z AUGUST 2020
TCPOD NUMBER…..20-065

I. ATLANTIC REQUIREMENTS
1. TROPICAL STORM ISAIAS
FLIGHT ONE – NOAA 49 FLIGHT TWO – TEAL 74
A. 01/0000Z A. 31/2330Z,01/0530Z
B. NOAA9 0909A ISAIAS B. AFXXX 1009A ISAIAS
C. 31/1730Z C. 31/2000Z
D. NA D. 23.0N 76.5W
E. NA E. 31/2300Z TO 01/0530Z
F. 41,000 TO 45,000 FT F. SFC TO 15,000 FT

FLIGHT THREE – NOAA 43 FLIGHT FOUR – NOAA 49
A. 31/2230Z A. 01/1200Z
B. NOAA3 1109A ISAIAS B. NOAA9 1209A ISAIAS
C. 31/2000Z C. 01/0530Z
D. 22.7N 76.0W D. NA
E. 31/2200Z TO 01/0400Z E. NA
F. SFC TO 15,000 FT F. 41,000 TO 45,000 FT

FLIGHT FIVE – NOAA 43 FLIGHT SIX – TEAL 75
A. 01/1000Z A. 01/1130Z,1730Z
B. NOAA3 1309A ISAIAS B. AFXXX 1409A ISAIAS
C. 01/0800Z C. 01/0830Z
D. 24.0N 78.0W D. 24.5N 78.5W
E. 01/0930Z TO 01/1530Z E. 01/1100Z TO 01/1730Z
F. SFC TO 15,000 FT F. SFC TO 15,000 FT

2. OUTLOOK FOR SUCCEEDING DAY:
A. BEGIN 3-HRLY FIXES AT 01/2030Z.
B. POSSIBLE NOAA P-3 TDR MISSIONS DEPARTING KLAL
AT 01/2000Z AND 02/0800Z.
C. POSSIBLE NOAA G-IV SYNOPTIC SURVEILLANCE MISSON AROUND
THE STORM FOR 02/0000Z, DEPARTING KLAL AT 01/1730Z.

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY…..NEGATIVE.

$$
WJM

NNNN

hurricane_guineapig
hurricane_guineapig
15 days ago

Isaias is looking quite good indeed on IR…
2020 is laughing at my attempts to predict what these storms will do.

isaias.jpg
IDTH
15 days ago

From Levi Cowan

Water vapor satellite imagery shows us how upper clouds are moving. An explosion of cirrus is emanating northwest from #Isaias in the last few hours. How much this outflow surge allows Isaias to fight the shear ahead of it will be key to how strong Isaias becomes in the Bahamas.”

https://twitter.com/TropicalTidbits/status/1288887767502598145?s=20

IDTH
15 days ago

Before I noted the best chances for intensification were if it’s just north of Hispaniola, allowing to be tightened quicker by the friction of the land and when it begins to feel the trough picking it up, allowing some potential baroclinic ventilation as it goes up the gulf stream.
It still has some shear in it’s way the next couple of days.

carmot
carmot
15 days ago

Oh snap, I said what??? When???
It’s good to be wromg. Yay me! ; )

Invest 93L comment.gif
hurricane_guineapig
hurricane_guineapig
15 days ago

Thank you for the post Dr.Masters!

Patrap
15 days ago

Band 13 – 10.3 µm – Clean Longwave Window – IR

2020212173723_GOES16-ABI-MESO-13-19N-69W-500x500.jpg
BarbaraGermany
BarbaraGermany
15 days ago
Reply to  Patrap

Long wave IR in motion:
comment image

BarbaraGermany
BarbaraGermany
15 days ago

Thanks for the update!

Latest TPW-loop:
comment image

Andre Brooks
Andre Brooks
15 days ago

Here we go

two_atl_2d1.png
17°61°
17°61°
15 days ago

Thanks for the update..

Andre Brooks
Andre Brooks
15 days ago

Let’s see if we have an ascat to show TS winds for 93L

Wyatt Washburn
Wyatt Washburn
15 days ago

CDO growing where the coc should form under, if it hasen’t already off the tip of the DR. You can see on water vapor the inflow racing into the southern notch of the growing strong convection. comment image

Andre Brooks
Andre Brooks
15 days ago

540
ABNT20 KNHC 301725
TWOAT

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
200 PM EDT Thu Jul 30 2020

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical
Storm Isaias, located over the northeastern Caribbean Sea.

Showers and thunderstorms associated with a small area of low
pressure, located a few hundred miles south-southeast of the Cabo
Verde Islands have increased and become better organized during the
day. Environmental conditions appear conducive for further
development, and this system could become a tropical depression
during the next day or so while it drifts generally
north-northwestward. After that time, environmental conditions are
forecast to become less favorable for development.
* Formation chance through 48 hours…medium…50 percent.
* Formation chance through 5 days…medium…50 percent.

&&
Public Advisories on Tropical Storm Isaias are issued under WMO
header WTNT34 KNHC and under AWIPS header MIATCPAT4.
Forecast/Advisories on Tropical Storm Isaias are issued under
WMO header WTNT23 KNHC and under AWIPS header MIATCMAT4.

$$
Forecaster Roberts

Caleb Hardee
Caleb Hardee
15 days ago

Thanks for the update!

terry
terry
15 days ago

hey guys start posting here more! hi gate!

terry
terry
15 days ago

Great post ! thanks for updates! been a while since i posted , but glad to see the blogs up and going!

surfdog pr
surfdog pr
15 days ago

rincon almost 20″inches wow thanks

Sunrisemama
Sunrisemama
15 days ago

Thank you Dr.Masters. So you’re thinking minimal TS conditions for South East Florida at this point?

Cthulhu Ferrigno
Cthulhu Ferrigno
15 days ago
Reply to  Sunrisemama

It’ll be really iffy to predict until it clears Hispanola and reforms a solid center of circulation.

FartingMoths
FartingMoths
15 days ago
Reply to  Sunrisemama

Like a moth farting in the breeze

Clayton Naquin
Clayton Naquin
15 days ago

Thanks for the update!

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