Tropical Storm Delta satellite image
GeoColor satellite image of Tropical Storm Delta southwest of Jamaica at 11:10 a.m. EDT Monday, October 5, 2020. (Image credit: RAMMB/CIRA/Colorado State University)

Tropical Storm Delta formed in the western Caribbean on Monday morning with the potential to rapidly intensify into a dangerous hurricane that will affect the Cayman Islands, northeast Mexico, and western Cuba on Tuesday and Wednesday and the central Gulf of Mexico coast of the U.S. on Thursday and Friday.

At 11 a.m. EDT Monday, Delta was headed west-northwest at seven mph, spreading heavy rain showers over Jamaica, Cuba, and the Cayman Islands, as seen on Cayman Islands radar. Satellite images showed Delta had nearly closed off a cloud-free center, and the storm was likely beginning to build an eyewall. Delta’s heavy thunderstorm activity was steadily growing more intense and expanding in areal coverage.

The first hurricane hunter mission into Delta is to occur Monday afternoon, and the first dropsonde mission by NOAA’s jet is scheduled for Tuesday afternoon.

The 2020 parade of record-early named storms continues

Delta’s October 5 arrival marks the earliest date that any Atlantic season has produced its 25th tropical storm, topping the record held by Gamma from November 15, 2005. In total, 22 of 2020’s 25 named storms set records for being the earliest-arriving for their respective letter; only Arthur, Bertha, and Dolly fell short.

With the Atlantic hurricane season three-quarters done, we’ve already had 25 named storms, eight hurricanes, two intense hurricanes, and an accumulated cyclone energy (ACE) index of 108 (26% above average for the date). Only one Atlantic hurricane season since 1851 has had more named storms during an entire season: 2005, with 28 named storms. According to Colorado State University hurricane scientist Phil Klotzbach, the averages for this point in the season are nine named storms, five hurricanes, two intense hurricanes, and an ACE index of 86.

Figure 1
Figure 1. Track forecasts out to eight days for Delta from the 6Z (2 a.m. EDT) Monday, October 5, run of the new version of the GFS ensemble model (GEFS). The black line is the mean of the 31 ensemble members; individual ensemble member forecasts are the thin lines, color-coded by the central pressure. Many of the 31 members called for Delta to hit the U.S. as a strong tropical storm or as a hurricane (orange and red colors). (Image credit: Tropical Tidbits)

Track forecast for Delta

The ridge of high pressure steering Delta will keep the storm on a west-northwest to northwest track at a forward speed between 7 – 16 mph through Wednesday, which will put the storm very near Grand Cayman Island between 6 and 10 a.m. EDT Tuesday, and near the western tip of Cuba or near the northeast tip of Mexico’s Yucatan Peninsula after 8 p.m. EDT Tuesday night.

Beginning on Tuesday night, Delta will draw close enough to Tropical Storm Gamma for the two storms to interact. When two tropical cyclones approach within about 900 miles of each other, they tend to rotate counter-clockwise around a common center, then go their separate ways, in a process called the Fujiwara effect.

In rare cases they may merge into one storm, but the resulting storm will not be stronger than either of the original two storms, as wind shear from each weakens the other. In the case of Delta and Gamma, Delta is likely to sling Gamma inland to the southeast over the Yucatan Peninsula, and Gamma is likely to push Delta on a more westerly track, closer to Texas. However, with Gamma now expected to make landfall in the Yucatan Peninsula on Tuesday, the storm may be small and weak enough that it will have only a negligible steering effect on Delta.

Once Delta enters the Gulf of Mexico on Wednesday, steering of the storm will be increasingly affected by a trough of low pressure over the south-central U.S.; the southwesterly winds will turn Delta sharply to the north or north-northeast on Wednesday night or Thursday morning. The exact timing and location of this turn are crucial for determining where on the U.S. coast Delta will make landfall. This turn cannot be predicted with accuracy this far in advance, as it will depend upon how much interaction Delta and Gamma have, and models make such forecasts poorly.

Figure 2
Figure 2. Predicted wind speed (colors) and sea level pressure (black lines) for Delta at 11 p.m. EDT Thursday, October 8, from the 6Z Monday, October 5, run of the HWRF model. The model predicted that Delta would be approaching the coast of Louisiana as a category 2 hurricane with 100 mph winds. (Image credit: Tropical Tidbits)

Intensity forecast for Delta

Delta will have nearly ideal conditions for intensification through Wednesday morning, with wind shear less than five knots, ocean temperatures of 30 degrees Celsius (86°F), and a moist atmosphere with a mid-level relative humidity of 70 – 75%. Delta will be passing over waters in the northwest Caribbean that have the highest heat content of any waters in the North Atlantic – an ideal setup for rapid intensification.

The top five intensity models predicted with at least one of their Monday morning runs that Delta would intensify into a hurricane by Wednesday, with a category 1 hurricane the dominant prediction. However, the 0Z Monday run of the top intensity model from 2019, the COAMPS-TC, predicted that Delta would peak as a category 4 hurricane on Wednesday in the southern Gulf of Mexico, and then weaken on approach to Louisiana.

The 12Z Monday run of the SHIPS model gave an unusually high probability that Delta will undergo rapid intensification: a 62% chance that it would intensify 75 mph by Thursday morning (12 times higher than the climatological odds). The official National Hurricane Center forecast called for Delta to achieve hurricane status on Tuesday afternoon, and become a category 2 hurricane by Wednesday morning. A reasonable uncertainty range for Delta’s intensity on Tuesday night and early Wednesday morning, during its closest approach to western Cuba and northeastern Mexico, is as a category 1 to category 3 hurricane.

By Thursday, when Delta will be approaching the U.S. Gulf Coast, the storm will encounter more hostile conditions for intensification. Waters beneath the storm will be significantly cooler, wind shear will rise, and dry air to the west of Delta will have the opportunity to wrap into its core. However, a strong band of upper-level winds to the north of Delta will provide a more efficient upper-level outflow channel as the storm approaches the coast, helping counteract the increased shear.

Both Sally and Laura encountered similar conditions when they made landfall earlier this year, and neither storm weakened before landfall. Delta could be anywhere between a strong tropical storm and a category 3 hurricane at landfall in the U.S., with the official NHC forecast of a category 2 hurricane with 100 mph winds a reasonable prediction.

The role of ocean heat content in Delta’s intensification

In the Gulf of Mexico, the deepest warm water is found in the Loop Current – an ocean current that transports warm Caribbean water through the Yucatan Channel between Cuba and Mexico. The current flows northward into the Gulf of Mexico, then loops southeastward just south of the Florida Keys (where it is called the Florida Current), and then goes just west of the westernmost Bahamas. From there, the waters of the Loop Current flow northward along the U.S. coast and become the Gulf Stream. During summer and fall, the Loop Current provides a deep (80 – 150 meter) layer of very warm water that can provide a huge energy source for a hurricane to rapidly intensify into a major hurricane.

The Loop Current commonly bulges out in the northern Gulf of Mexico and sometimes will shed a clockwise rotating ring of warm water that separates from the main current. This ring of warm water slowly drifts west-southwestward towards Texas or Mexico at between two and three miles per day. This feature is called a “Loop Current ring”, “Loop Current eddy”, or “warm core ring”, and it can provide a key source of energy to fuel rapid intensification of hurricanes that cross the Gulf (in addition to the Loop Current itself).

Extreme events ‘presage worse to come’ in a warming climate

In 2020, fortunately, no warm Loop Current eddy is present in the central Gulf (though there is a weak warm eddy in the western Gulf). Instead, a prominent counter-clockwise rotating cool eddy lies in the central Gulf. The current track forecast calls for Delta to pass along the southern edge of that cool eddy, which may slow the intensification process. Once Delta approaches the U.S. Gulf Coast, the storm will encounter another region of cool waters caused by cool air flowing over the Gulf over the past week in the wake of the passage of the season’s first major cold front. Near the Florida-Alabama border, waters have also been cooled by the passage of Hurricane Sally in mid-September.

Figure 3
Figure 3. Ocean Heat Content (OHC) levels in the western Caribbean and Gulf of Mexico on October 4, 2020. The warm waters of the Loop Current lay near the western tip of Cuba, and Delta is expected to pass over this high heat content water before moving along the southern edge of a cool eddy with limited heat content in the central Gulf. OHC values higher than 75 kilojoules per square centimeter (light green colors) are highly favorable for rapid intensification of hurricanes. Near-shore waters along the continental shelf are too shallow to have a relevant number for OHC, and are left white in this image. (Image credit: University of Miami Rosenstiel School of Marine and Atmospheric Science)

Gamma expected to make a second landfall in Mexico’s Yucatan Peninsula

Tropical Storm Gamma made landfall in Mexico’s Yucatan Peninsula early Saturday afternoon with top winds of 70 mph, just below hurricane strength, bringing heavy rains to portions of the Yucatan Peninsula, western Cuba, and Central America.

According to Conagua, 24-hour rainfall amounts of 11.41 inches of rain were recorded at Tizimin, and 9.63 inches at Cozumel. At 11 a.m. EDT Monday, Gamma was over the southern Gulf of Mexico, just off the coast of the Yucatan Peninsula, with top winds of 45 mph, moving south-southwest at 2 mph.

Forecast for Gamma

Conditions for development of Gamma will be unfavorable through Wednesday, with high wind shear of 15 – 30 knots and a dry atmosphere (a mid-level relative humidity of 50 – 60%). The top intensity models and the official NHC forecast all predict slow weakening of Gamma through Wednesday. This process will be hastened if Gamma makes landfall over the Yucatan Peninsula on Tuesday, as predicted by NHC.

Gamma, caught in an area of weak steering currents, is expected to move at less than 5 mph for the remainder of its existence, resulting in heavy rains across much of Mexico’s Yucatan Peninsula and portions of Central America.

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Posted on October 5, 2020 (1:21 pm EDT).

Topics: Weather Extremes
326 Comments
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Art
Art
22 days ago

BULLETIN
Hurricane Delta Intermediate Advisory Number 9A…Corrected
NWS National Hurricane Center Miami FL AL262020
800 PM EDT Tue Oct 06 2020

Corrected distance from Cozumel

…EXTREMELY DANGEROUS CATEGORY FOUR HURRICANE DELTA HEADING
TOWARD THE NORTHEASTERN COAST OF THE YUCATAN PENINSULA…
…EXPECTED TO BRING A LIFE-THREATENING STORM SURGE AND EXTREME
WINDS…

SUMMARY OF 800 PM EDT…0000 UTC…INFORMATION
———————————————-
LOCATION…19.2N 84.5W
ABOUT 180 MI…290 KM ESE OF COZUMEL MEXICO
MAXIMUM SUSTAINED WINDS…145 MPH…230 KM/H
PRESENT MOVEMENT…WNW OR 300 DEGREES AT 17 MPH…28 KM/H
MINIMUM CENTRAL PRESSURE…956 MB…28.23 INCHES

WATCHES AND WARNINGS
——————–
CHANGES WITH THIS ADVISORY:

Beneteauman
Beneteauman
23 days ago

Does anyone see any westward movement in models,,into LA, East Texas state line?

Skyepony
23 days ago

Cat 4 Delta..

10061640Delta.png
Art
Art
23 days ago
Reply to  Skyepony

gee skye this is a Dangerous hurricane, I hope people in its projected path heed the NHC warnings and prepare

Skyepony
23 days ago
Hurricane Delta Tropical Cyclone Update
NWS National Hurricane Center Miami FL       AL262020
1120 AM EDT Tue Oct 06 2020

...RECENTLY RECEIVED DATA FROM A NOAA HURRICANE HUNTER AIRCRAFT 
INDICATE THAT DELTA HAS RAPIDLY STRENGTHENED INTO A CATEGORY 4 
HURRICANE...

Data from a NOAA Hurricane Hunter aircraft indicate that Delta is 
continuing to rapidly strengthen. The maximum winds have 
increased to near 130 mph (215 km/h) with higher gusts.  This makes 
Delta a category 4 hurricane on the Saffir-Simpson Hurricane Wind 
Scale.


SUMMARY OF 1120 AM EDT...1520 UTC...INFORMATION
---------------------------------------------------
LOCATION...18.2N 82.7W
ABOUT 315 MI...510 KM ESE OF COZUMEL MEXICO
ABOUT 125 MI...200 KM SW OF GRAND CAYMAN
MAXIMUM SUSTAINED WINDS...130 MPH...215 KM/H
PRESENT MOVEMENT...WNW OR 300 DEGREES AT 16 MPH...26 KM/H
MINIMUM CENTRAL PRESSURE...954 MB...28.17 INCHES

$$
Forecaster Brown
Jessica BSW
Jessica BSW
23 days ago

hello, ill be here from now

Mary Battle
Mary Battle
23 days ago

If the hurricane turns annular, does that mean it is less likely to weaken on approach to LA?

White Rabbit
White Rabbit
23 days ago
Reply to  Mary Battle

Yes, due to laws of thermodynamics, conservation of motion, etc. some force has to act on the wind to slow it down. An annular storm has a lot of momentum. It’s more a matter of needing something to stop the winds at that point. A weaker storm might be helped by fuel (hot water, moist air) whereas a strong storm is already moving so fast that it will take more to spin it down. Hope that makes sense.

Last edited 23 days ago by White Rabbit
Naturefiles
Naturefiles
23 days ago

Is Disqus dead?

DOOM Cat
DOOM Cat
23 days ago

LOL @ the intensity guidance displayed graphically as part of this OP

Scott Tribe
Scott Tribe
23 days ago

…RECENTLY RECEIVED DATA FROM A NOAA HURRICANE HUNTER AIRCRAFT INDICATE THAT DELTA HAS RAPIDLY STRENGTHENED INTO A CATEGORY 4 HURRICANE…

Scott Tribe
Scott Tribe
23 days ago
Reply to  Scott Tribe

000
WTNT61 KNHC 061520
TCUAT1

Hurricane Delta Tropical Cyclone Update
NWS National Hurricane Center Miami FL    AL262020
1120 AM EDT Tue Oct 06 2020

…RECENTLY RECEIVED DATA FROM A NOAA HURRICANE HUNTER AIRCRAFT 
INDICATE THAT DELTA HAS RAPIDLY STRENGTHENED INTO A CATEGORY 4 
HURRICANE…

Data from a NOAA Hurricane Hunter aircraft indicate that Delta is 
continuing to rapidly strengthen. The maximum winds have 
increased to near 130 mph (215 km/h) with higher gusts. This makes 
Delta a category 4 hurricane on the Saffir-Simpson Hurricane Wind 
Scale.

SUMMARY OF 1120 AM EDT…1520 UTC…INFORMATION
—————————————————
LOCATION…18.2N 82.7W
ABOUT 315 MI…510 KM ESE OF COZUMEL MEXICO
ABOUT 125 MI…200 KM SW OF GRAND CAYMAN
MAXIMUM SUSTAINED WINDS…130 MPH…215 KM/H
PRESENT MOVEMENT…WNW OR 300 DEGREES AT 16 MPH…26 KM/H
MINIMUM CENTRAL PRESSURE…954 MB…28.17 INCHES

Michael
Michael
23 days ago

Where did everyone go? I miss the days of having an open discussion with hundreds and hundreds of comments.

horace
horace
23 days ago

what happened to disqus? did they move somewhere else?

akarimorph
akarimorph
23 days ago
Reply to  Skyepony (mod)

I love you for posting this! I was so bummed last night when nobody had posted on here for a half hour..

JCheeverLoophole42
JCheeverLoophole42
23 days ago
Reply to  Skyepony (mod)

Many thanks for posting the link, Skye.

David
David
23 days ago
Reply to  Skyepony (mod)

It doesnt work for me “We were unable to load the disqus”

fyrebyrd042
fyrebyrd042
23 days ago
Reply to  Skyepony (mod)

Yea doesn’t work for me anymore.

Skyepony
23 days ago
Reply to  horace

Read down below, there is a link to the WU disqus backdoor.

Last edited 23 days ago by Skyepony (mod)
akarimorph
akarimorph
23 days ago
Reply to  Skyepony

looks like the link doesnt work now.. 🙁

Pablo Lopez
Pablo Lopez
23 days ago

Seems like Texas needs to keep a bit of a watch on Delta eh? As per 2020 rules? Also, I miss Disqus… 🙁

White Rabbit
White Rabbit
23 days ago
Reply to  Pablo Lopez

Everyone in the GOM needs to watch 100%. It’s way too early right now to rule anything in or out.

Patrap
Patrap
23 days ago

Viz loop
comment image

07e3fd9588e7d86d84f9395052a7e1fa.jpg
White Rabbit
White Rabbit
23 days ago

Sunday Night – Invest, Monday morning, Hurricane, Tuesday Morning, MAJOR.

If you look at the Euro, it predicts a scary storm. GFS predicts an annular major. NAMS predicts you better start saying your prayers and making your will. WOW

Patrap
Patrap
23 days ago
Reply to  White Rabbit

Lighten up Francis.

Folks I. The cone are watching g carefully.

four waters
four waters
23 days ago
Reply to  Patrap

Hey Pat… Hope yer well, and smoke is better now. Stay safe.

White Rabbit
White Rabbit
23 days ago
Reply to  Patrap

I didn’t thumbs-down you, btw. My post was meant more as gallows humor. I’m in the path, and it helps with the stress. 🙂

Skyepony
23 days ago
Reply to  Patrap

Have some NAVGEM…

100606zNavgem.png
ChanceShowerLA
ChanceShowerLA
23 days ago

Delta….
comment image?hash=65237

Scott Gillilan
Scott Gillilan
23 days ago
Reply to  ChanceShowerLA

Not good. I swear, this year…is so challenging. Wherever this lands it won’t be pretty.

Art
Art
23 days ago
Based on 0600 UTC surface analysis and satellite imagery through 
1000 UTC.

...SPECIAL FEATURES...

Hurricane Delta continues to intensify near 17.5N 81.3W at 
06/0900 UTC or 360 nm ESE of Cozumel Mexico moving WNW at 13 kt. 
Estimated minimum central pressure is 968 mb. Maximum sustained 
wind speed is 85 kt with gusts to 105 kt. Numerous strong
convection is ongoing within 75 nm of the center of Delta. in
addition, outer bands on the south side of Delta are evident, with
strong thunderstorms active within 120 nm off the coast of eastern
Honduras and northeast Nicaragua. Seas are rapidly building near
the center of Delta as the winds increase, and maximum wave
heights are estimated to be 20 to 25 ft. Delta will become a major hurricane
as moves through the northwest Caribbean this afternoon, and 
will pass into through the Yucatan Channel and northeast tip of
the Yucatan Peninsula tonight before it enters into the south- 
central Gulf of Mexico. Delta will continue across the central 
Gulf through mid week and is expected to make landfall in 
Louisiana by late Fri or early Sat. Please read the latest NHC 
Public Advisory at https://www.nhc.noaa.gov/text/MIATCPAT1.shtml 
and Forecast/ Advisory at 
https://www.nhc.noaa.gov/text/MIATCMAT1.shtml for more details.
Art
Art
23 days ago
000
FXUS62 KTBW 061206
AFDTBW

Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
806 AM EDT Tue Oct 6 2020

.UPDATE...
The areas of low clouds and some fog from around the Interstate 4
corridor northward early this morning will lift and dissipate by
mid-morning. Then with daytime heating we`ll see scattered to
numerous showers and a few thunderstorms develop this afternoon
moving west out into the eastern gulf during this evening. Highest
rain chances will be across the southern interior and southwest
Florida mid-afternoon into early this evening where moisture is
deepest. Partly to mostly cloudy skies are then expected overnight
with some more areas of low clouds and fog possible toward
morning, especially across the Nature Coast. Current forecast
looks on track with no major changes planned.

&&
Skyepony
23 days ago

10062020 06z RI probabilities for Delta..
comment image?w=800&h=175

NCHurricane2009
23 days ago

Also note the WMO has no plans to retire the name Delta, someone on the disqus blog had sent me a neat article on the matter (in 2006 it had been decided greek names occur infrequently enough that there are no plans to retire a greek name officially).

Cthulhu Ferrigno
Cthulhu Ferrigno
23 days ago

It’s still unprecedented. I’m sure there will have to be some kind of official determination to retire or not.

Last edited 23 days ago by Cthulhu Ferrigno
NCHurricane2009
23 days ago

Good morning to you all, Delta has continued to overachieve in the overnight, I had to do multiple special updates throughout the afternoon and evening, in my latest update at this link from around midnight I am thinking Delta will become a major cat 3+ hurricane later today, and indeed while waking up this morning Delta is on the cusp of cat 3.