Tropical Storm Delta Forms, Rapidly Intensifying

Tropical Storm Delta formed early Monday morning in the far Western Carribean. Over the last several hours, Delta has been rapidly intensifying, with this continuing over the next 48 hours.

Based on the forecast track, the Cayman Islands, parts of Mexico and Cuba may face Delta’s strongest winds and rainfall as tropical storm and hurricane warnings are already in effect.

Delta is forecast to become the 9th hurricane of the 2020 Atlantic Hurricane Season and the third hurricane that may reach major hurricane status.

This tropical cyclone has become the 26th tropical cyclone of the 2020 Atlantic Hurricane Season and the earliest 25th named storm in Atlantic history. The previous record for the 25th named storm was Gamma, on November 15th, 2005. The last (and only) time Delta was used in the Atlantic was on November 22nd, 2005.

This tropical cyclone is not forecast to impact Trinidad, Tobago, or the Lesser Antilles.

List of names for the 2020 Atlantic Hurricane Season. The next named tropical cyclone will be called Epsilon.
List of names for the 2020 Atlantic Hurricane Season. The next named tropical cyclone will be called Epsilon.

At 5:00 PM AST, the center of Tropical Storm Delta was located near latitude 16.2 North, longitude 79.4 West. Delta is moving toward the west near 8 mph (13 km/h), and a turn toward the west-northwest should occur this evening. A faster northwestward motion is expected Tuesday through Wednesday night. On the forecast track, the center of Delta is expected to pass southwest of the Cayman Islands early Tuesday, and approach the northeastern portion of the Yucatan peninsula and the Yucatan Channel Tuesday afternoon or evening. Delta is forecast to move into the southern Gulf of Mexico Tuesday night or early Wednesday, and be over the south-central Gulf of Mexico on Wednesday and Wednesday night.

Data from a NOAA Hurricane Hunter aircraft indicate that the maximum sustained winds have rapidly increased to near 70 mph (110 km/h) with higher gusts. Additional rapid strengthening is expected during the next day or so, and Delta is expected to be a major hurricane when it nears the Yucatan Peninsula.

Tropical-storm-force winds extend outward up to 70 miles (110 km) from the center. The minimum central pressure estimated from NOAA reconnaissance aircraft data is 983 millibars.

Tropical Storm Delta Forecast Track as of 5:00 PM AST Monday 5th October 2020. (National Hurricane Center)
Tropical Storm Delta Forecast Track as of 5:00 PM AST Monday 5th October 2020. (National Hurricane Center)

Watches & Warnings

Tropical Storm Delta Watches and Warnings as of 5:00 PM Monday 5th October 2020. (National Hurricane Center)

A Hurricane Warning is in effect for:

  • Cuba province of Pinar del Rio
  • Tulum to Rio Lagartos Mexico
  • Cozumel

A Hurricane Watch is in effect for:

  • Cuban province of Artemisa
  • Isle of Youth

A Tropical Storm Warning is in effect for:

  • Cayman Islands including Little Cayman and Cayman Brac
  • Isle of Youth

A Tropical Storm Watch is in effect for:

  • Cuba province of La Habana

A Hurricane Warning means that hurricane conditions are expected somewhere within the warning area. A warning is typically issued 36 hours before the anticipated first occurrence of tropical-storm-force winds, conditions that make outside preparations difficult or dangerous. Preparations to protect life and property should be rushed to completion.

A Hurricane Watch means that hurricane conditions are possible within the watch area, generally within 48 hours.

A Tropical Storm Warning means that tropical storm conditions are expected somewhere within the warning area within 36 hours.

A Tropical Storm Watch means that tropical storm conditions are possible within the watch area, generally within 48 hours.

For storm information specific to your area, please monitor products issued by your national meteorological service.

Hazards Affecting Land

Tropical Storm Delta probabilities for tropical-storm-force winds as of 5:00 PM AST Monday 5th October 2020, as well as the most likely time of arrival of tropical-storm-force winds. (National Hurricane Center)
Tropical Storm Delta probabilities for tropical-storm-force winds as of 5:00 PM AST Monday 5th October 2020, as well as the most likely time of arrival of tropical-storm-force winds. (National Hurricane Center)

STORM SURGE: A dangerous storm surge will raise water levels by as much as 4 to 7 feet above normal tide levels along coast of the Yucatan peninsula within the hurricane warning area, near and to right of where the center makes landfall. Near the coast, the surge will be accompanied by large and dangerous waves.

WIND: Tropical storm conditions are expected in the Cayman Islands beginning tonight. Hurricane conditions are expected within the hurricane warning area in the Yucatan Peninsula Tuesday night, with tropical storm conditions beginning late Tuesday. Hurricane conditions are expected within a portion of the Hurricane Warning area in western Cuba by late Tuesday night, with tropical storm conditions expected beginning late Tuesday. Hurricane conditions are possible on the Isle of Youth beginning Tuesday afternoon with tropical storm conditions expected by early Tuesday. Tropical storm conditions are possible in the Tropical Storm Watch area in Cuba on Tuesday.

RAINFALL: Through midweek, Delta is expected to produce 3 to 6 inches of rain with isolated maximum totals of 8 inches across Jamaica, the Cayman Islands, western Cuba, and the northern Yucatan Peninsula. This rainfall could lead to significant flash floods and mudslides.

Later this week into the weekend, Delta is expected to bring heavy rainfall across portions of the central Gulf Coast into the southeastern United States.

This system is of no direct threat to the Windward Islands, including Trinidad and Tobago.

Tropical Storm Delta Forecast Discussion

Potential Tropical Cyclone Twenty-Six (Weathernerds.org)

Visible satellite imagery shows that the convective banding of Delta has continued to quickly improve since this morning. The primary convective band now wraps entirely around the center, with what appears to be a banding-type eye feature occasionally noted. There are some dry slots between the convective bands but those appear to be gradually filling in. A NOAA Hurricane Hunter aircraft currently collecting data in the storm environment found peak SFMR winds of 55 kt during its first pass through the center from northwest to southeast. The plane also reported a minimum pressure of 983 millibars, much lower than previously estimated. The aircraft also observed an 18 nautical mile-wide-eye that was open to the west-northwest. Assuming that there are stronger winds yet to be sampled in the northeastern quadrant, the initial intensity has been raised to 60 kt.

Delta is situated within a very conducive environment for strengthening. The storm will be moving over SSTs of 29-30 degrees Celsius and the vertical wind shear is forecast to remain 5 kt or less while Delta traverses the northwestern Caribbean. These conditions are expected to allow for rapid strengthening over the next 24 to 36 hours. The SHIPS Rapid Intensification Index gives a better than 50 percent chance of a 35-40 kt increase in wind speed over the next 24 hours. The NHC intensity forecast follows suit by calling for rapid intensification over the next day or so, and Delta is forecast to be a major hurricane when it passes near or over the northeastern portion of the Yucatan peninsula. Once the storm reaches the central Gulf of Mexico in 60-72 hours, increasing southwestern vertical wind shear and cooler shelf waters over the northern Gulf are likely to result in some reduction in wind speed as the system nears the northern Gulf coast. Although there is still significant uncertainty regarding Delta’s intensity when it nears the northern Gulf coast, it is becoming increasingly likely that the system will pose a significant wind and storm surge threat to a portion of that area.

The center has jogged southward again this afternoon, which appears to be primarily due to the system organizing rather than a true storm motion. The initial motion estimate remains an uncertain 275/7 kt. Delta should begin moving west-northwestward this evening, and a west-northwestward to northwestward motion around the southwestern portion of a deep-layer ridge to its northeast is expected over the next couple of days. The more southward initial position and more ridging over the eastern Gulf of Mexico has resulted in a significant westward shift in the track envelope through the first 60-72 hours. The NHC has been adjusted in that direction, and this has required the issuance of a Hurricane Warning for the northeastern portion of the Yucatan peninsula of Mexico. After 72 hours, a mid- to upper-level trough is forecast to develop over Texas which should cause Delta to turn northward and then north-northeastward toward the northern Gulf Coast. Although the track forecast has not changed much during the latter portion of the period, there is more cross-track spread in the model guidance than before, which has increased the uncertainty regarding potential landfall and the timing of Delta’s approach to the northern Gulf Coast.

Key Messages:

  1. Dangerous storm surge and hurricane conditions are expected within portions of the northern Yucatan Peninsula of Mexico and are possible in extreme western Cuba beginning Tuesday night, and a Hurricane Warning is in effect.
  2. Heavy rainfall will affect portions of Jamaica, the Cayman Islands, western Cuba and the northern Yucatan Peninsula during the next few days. This rainfall could lead to significant flash flooding and mudslides.
  3. Tropical storm conditions are expected in portions of the Cayman Islands beginning tonight or early Tuesday, and a Tropical Storm Warning is in effect.
  4. Delta is forecast to approach the northern Gulf Coast late this week as a hurricane. While there is large uncertainty in the track and intensity forecasts, there is an increasing risk of dangerous storm surge, wind, and rainfall hazards along the coast from Louisiana to the western Florida Panhandle beginning Thursday night or Friday. Residents in these areas should ensure they have their hurricane plan in place and monitor updates to the forecast of Delta.

Forecast discussion by NHC Forecaster Brown.

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