Sunrise from underneath Hurricane Delta's central dense overcast on Oct. 7, 2020, from NOAA Hurricane Hunter aircraft Kermit, flying at 10,000 feet. (Image credit: Paul Chang, NOAA)

Hurricane Delta weakened significantly before making landfall at 6:30 a.m. EDT Wednesday, October 7, near Puerto Morelos, Mexico – 20 miles south of Cancun – as a category 2 storm with 110 mph winds. Delta, emerging into the Gulf of Mexico early Wednesday afternoon, is expected to re-intensify before turning to the north on Thursday night and making landfall in Louisiana on Friday. A hurricane watch and storm surge watch are in effect from High Island, Texas, to Grand Isle, Louisiana, with the storm surge watch extending to the Alabama-Florida border.

At landfall on Wednesday morning in Mexico, a WeatherFlow observing site in Cancun, located in the stronger right eyewall of Delta, recorded sustained winds of 84 mph, gusting to 106 mph. Buoy 42056, located 138 miles southeast of Cozumel, went through Delta’s weaker southern eyewall on Wednesday morning. At midnight EDT, the buoy recorded sustained winds of 74 mph, gusting to 92 mph. Storm chasers Reed Timmer and Josh Morgerman documented by videos posted to Twitter considerable, but not catastrophic, damage in Cancun from Delta.

Figure 1. GeoColor satellite image of Hurricane Delta at 11 a.m. EDT Wednesday, October 7. (Image credit: RAMMB/CIRA/Colorado State University)

Rapid intensification, then rapid weakening, before landfall in Mexico

At landfall in Mexico, Delta remained a relatively small hurricane, with hurricane-force winds extending out 30 miles from the center and tropical storm-force winds extending out 140 miles. Small hurricanes, given their less mass to accelerate or decelerate when conditions for intensification change, are prone to rapid changes in intensity. Because of its small size and the near-ideal conditions for intensification, Delta was able to put on a rare feat of rapid intensification, going from a tropical depression with 35 mph winds at 5 a.m. EDT Monday to a category 4 hurricane with 145 mph winds at 5 p.m. EDT Tuesday.

Also see: Climate change is causing more rapid intensification of Atlantic hurricanes

However, on Tuesday evening, the Hurricane Hunters documented that a sneak attack on Delta’s southeast flank was occurring. As shown by Andy Hazelton, a narrow but strong burst of mid-level winds, blowing at up to 70 mph, impinged on the hurricane’s southeast side. These winds were strong enough to thoroughly disrupt the intense but relatively fragile hurricane, resulting in a complete collapse of Delta’s eyewall late Tuesday evening. As a result, Delta weakened from a category 4 to a category 2 hurricane before landfall in Mexico, sparing Cancun a more serious hit.

Figure 2. Track forecast out to eight days for Delta from the 6Z (2 a.m. EDT) Wednesday, October 7, run of the COAMPS-TC ensemble model. The individual ensemble member forecasts are color-coded by Saffir-Simpson category. Most of the forecasts called for Delta to hit the U.S. as a category 2 or 3 hurricane, with a few predicting a category 1 or category 4 storm at landfall. The COAMPS-TC model was the top-performing intensity model and the third-best track model of 2019 (behind the European and UKMET models). (Image credit: Navy Research Lab, Monterey)

Track forecast for Delta

Steering of Delta on Wednesday and Thursday will be controlled by a ridge of high pressure to the storm’s northeast, which will keep Delta on a northwesterly track across the Gulf of Mexico. By Thursday night, Delta will draw close enough to a trough of low pressure over the south-central U.S. to begin being affected by the southwesterly winds of the trough. These winds will turn Delta sharply to the north and then north-northeast. The exact timing and location of this turn are crucial for determining where on the U.S. coast Delta will make landfall. A stronger Hurricane Delta will be more likely to turn sooner and make landfall farther to the east, over central Louisiana. A weaker storm will make the turn later, with landfall closer to the Texas-Louisiana border.

Figure 3. Predicted wind speed (colors) and sea level pressure (black lines) for Hurricane Delta at 2 p.m. EDT (18Z) Friday, October 9, from the 6Z Wednesday, October 7, run of the HWRF model. The model predicted Delta would be approaching Louisiana as a high-end category 2 hurricane with 110 mph winds. (Image credit: Tropical Tidbits)

The European model, normally the best-performing track model, has the most westerly track, predicting a weaker storm and a landfall near the Texas-Louisiana border. However, this model does not make reliable intensity forecasts, and the intensity of Delta has to be correctly modeled in order to make a good track forecast in this case. The European model was out-performed by most of the other top track models during a similar situation during the landfall of Hurricane Laura in western Louisiana in late August (see more on Laura below).

The most likely landfall location from Delta therefore is in central Louisiana, as predicted by other top track models – the GFS, UKMET, COAMPS-TC, NAVGEM, and HWRF – and by the official National Hurricane Center forecast. It now appears that Mississippi and Alabama, which are no longer in the NHC cone of uncertainty, are at low risk of a direct strike. If the model consensus is accurate, Delta could make landfall near Lafayette, Louisiana, (metro population about 500,000). In a 2016 analysis by 24/7 Wall St., Lafayette was rated the 15th most vulnerable city to residential damage from hurricanes, and the second most vulnerable in Louisiana after New Orleans.

The NHC cone of uncertainty for Delta includes Lake Charles, Louisiana – the sixth time in 2020 this has occurred (with Cristobal, Laura, Marco, Sally, and Beta being the other storms). Thanks go to Heather Marie Zons for this stat.

Figure 4. Predicted rainfall amounts from the 6Z (2 a.m. EDT) Wednesday, October 7, run of the experimental HAFS model, for the four-day period ending at 6Z Sunday, October 11. The model predicted that Delta would dump more than 10 inches of rain (yellow-brown colors) in much of Louisiana. (Image credit: NOAA/AOML)

Intensity forecast for Delta

Passage of Delta over the tip of the Yucatan Peninsula will disrupt the hurricane, potentially resulting in a weakening by a full Saffir-Simpson category. However, the terrain Delta will be passing over is not mountainous, and the hurricane likely will emerge over the Gulf of Mexico fundamentally intact.

In the southern Gulf of Mexico, Delta will be over shallow continental shelf waters with relatively low heat content; these waters will have also cooled as a result of the passage of Tropical Storm Gamma over the weekend. However, by Wednesday evening, Delta will be back over warm, deep waters with high heat content, providing it high-octane fuel through Thursday. Wind shear is predicted to be a low to moderate 5 – 15 knots through Thursday, and during this period, Delta likely will steadily intensify, peaking as a category 3 or 4 storm. Delta will also expand in size, with NHC predicting over a 25% expansion in the area experiencing tropical storm-force winds. It is possible that some of this enlargement will occur because Delta absorbed some of the spin from ex-Tropical Storm Gamma, which was over the Yucatan Peninsula when Delta made landfall. The expected increase in Delta’s size likely will lead to a large section of the U.S. Gulf Coast’s experiencing a damaging storm surge at landfall, with NHC predicting a storm surge of between seven and eleven feet.

Figure 5. Ocean Heat Content (OHC) levels on October 7, with the 5 a.m. EDT advisory positions for Hurricane Delta overlaid. Delta will then move over continental shelf waters with limited heat content on Wednesday afternoon, but once in the central Gulf, will encounter OHC values of 50 – 75 kilojoules per square centimeter (light green colors). OHC values in excess of 75 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 black in this image. (Image credit: University of Wisconsin CIMSS)

On Friday, conditions for intensification will grow more hostile. Ocean temperatures beneath Delta will be 27 – 28 degrees Celsius (81 – 82°F), the atmosphere will dry to a mid-level relative humidity of 60%, and wind shear will rise to a high of 20 to 30 knots. This high wind shear may be able to inject dry air to Delta’s west into its core, significantly weakening the storm. 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. In addition, Delta will be a larger storm better able to resist high wind shear and dry air.

Sally and Laura both encountered similar conditions when they made landfall earlier this year, and neither storm weakened before landfall (though they had warmer ocean temperatures to work with near the coast). The top intensity models generally predicted with their Wednesday morning runs that Delta would be a category 2 or 3 hurricane at the time of landfall on the U.S. northern Gulf Coast. Delta likely will be a highly destructive storm, with significant threats from wind damage, heavy rains, and storm surge.

Figure 6. National Guard troops respond in the aftermath of Hurricane Laura in Lake Charles, Louisiana. The Capital One Tower in the background had many of its windows blown out. (Photo credit: Josiah Pugh)

Louisiana still recovering from Hurricane Laura

Hurricane Laura on August 27 roared ashore in western Louisiana as a mighty category 4 storm with 150 mph winds – the strongest landfalling hurricane in Louisiana history, and the fifth-strongest hurricane on record to make a continental U.S. landfall.

Laura brought a storm surge as high as 17.2 feet above dry ground (20 feet above sea level) to Rutherford Beach, Louisiana, ranking as the ninth-highest storm surge on record for the Gulf Coast. In its wake, Laura left 33 people dead in the U.S. and over $10 billion in damage, with Lake Charles, Louisiana, suffering some of the most severe impacts. In the wake of that recent damage, Hurricane Delta now is predicted to affect many of the areas still recovering from Laura.

Bob Henson contributed to this post.

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Posted on October 7, 2020 (1:43pm EDT).

Jeff Masters

Jeff Masters, Ph.D., worked as a hurricane scientist with the NOAA Hurricane Hunters from 1986-1990. After a near-fatal flight into category 5 Hurricane Hugo, he left the Hurricane Hunters to pursue a...

63 replies on “Hurricane Delta takes aim at U.S. Gulf Coast”

  1. Looks like as we pass noon Hurricane Delta is finally redeveloping a new eye, probably on its way to cat 3 later today, but I think there could be enough shear to weaken Delta back to cat 2 for its landfall in Louisiana tomorrow night. Regardless of which category the hurricane falls into at landfall, a hurricane is a dangerous storm with coastal storm surge potential, heavy flash flooding rains, and winds strong enough to cause damage, so keep that in mind.

    My latest birdseye view chart and post discussing Hurricane Delta further and also a couple of other areas to watch for in the Atlantic is at this link.

  2. Morning everyone…..what’s that starting to take shape in Delta….also notice the trough over TX pushing east….

      1. White Rabbit, With your name it is a humorous play on words to say to keep our eyes wide open. I’ll tell Alice. You are right about the warning.

  3. The aircraft and fairly recent scatterometer data indicate that
    Delta is gradually growing in size. This trend is expected to
    continue as Delta approaches the Louisiana coast. The NHC wind
    radii forecast follows a consensus of the global and hurricane
    regional models.

    Key Messages:

    1. Delta is expected to grow in size as it approaches the northern
    Gulf Coast, where life-threatening storm surge and dangerous
    hurricane-force winds are likely beginning Friday, particularly for
    portions of the Louisiana coast. Storm Surge and Hurricane Warnings
    are in effect, and residents in these areas should follow advice
    given by local officials and rush preparedness actions to
    completion.

    2. Significant flash, urban, small stream and minor to isolated
    moderate river flooding is likely Friday and Saturday from portions
    of the central Gulf Coast into portions of the Lower Mississippi
    Valley. As Delta moves farther inland, heavy rainfall is expected in
    the Ohio Valley and Mid-Atlantic this weekend.

    FORECAST POSITIONS AND MAX WINDS

    INIT 08/0900Z 23.4N 91.8W 85 KT 100 MPH
    12H 08/1800Z 24.6N 93.0W 95 KT 110 MPH
    24H 09/0600Z 26.4N 93.7W 100 KT 115 MPH
    36H 09/1800Z 28.8N 93.4W 90 KT 105 MPH
    48H 10/0600Z 31.3N 92.4W 55 KT 65 MPH…INLAND
    60H 10/1800Z 33.3N 90.9W 30 KT 35 MPH…INLAND
    72H 11/0600Z 34.6N 89.0W 20 KT 25 MPH…POST-TROP/REMNT LOW
    96H 12/0600Z…DISSIPATED

    $$
    Forecaster Cangialosi

  4. Japan Meteorological Agency
    Tropical Cyclone Advisory #31 – 15:00 PM JST October 8 2020
    TYPHOON CHAN-HOM (T2014)
    ==================================================
    280 km southeast of Tanegashima (Kagoshima Prefecture)

    At 6:00 AM UTC, Typhoon Chan-hom (970 hPa) located at 28.7N 132.9E has 10 minute sustained winds of 65 knots with gusts of 95 knots. The cyclone is reported as moving north at 8 knots.

    Storm Force Winds
    ===================
    90 nm from the center in northwestern quadrant
    60 nm from the center in southeastern quadrant

    Gale Force Winds
    ==================
    240 nm from the center in northwestern quadrant
    210 nm from the center in southeastern quadrant

    Dvorak Intensity: T4.5-

    Forecast and Intensity
    =========================
    24 HRS: 30.8N 133.1E – 70 knots (CAT 3/Strong Typhoon) 200 km east of Tanegashima (Kagoshima Prefecture)
    48 HRS: 33.3N 136.3E – 65 knots (CAT 3/Strong Typhoon) 50 km east southeast of Shionomisaki (Wakayama Prefecture)
    72 HRS: 36.4N 145.0E – 55 knots (CAT 2/Severe Tropical Storm) Sea East of Japan (Ibaraki Prefecture)

    1. Still seems to be going WNW, based on the coordinates. Maybe going west of forecast track, unless it turns more sharply?

  5. Great articles on Delta, Docs; as always. Thankee.

    And especially Thank You for the lead photos for the articals. Absolutely breathtaking.

  6. Japan Meteorological Agency
    Tropical Cyclone Advisory #29 – 9:00 AM JST October 8 2020
    TYPHOON CHAN-HOM (T2014)
    ==================================================
    340 km East of Amami Oshima (Kagoshima Prefecture)

    At 0:00 AM UTC, Typhoon Chan-hom (970 hPa) located at 27.9N 132.9E has 10 minute sustained winds of 65 knots with gusts of 95 knots. The cyclone is reported as moving north at 7 knots.

    Storm Force Winds
    ===================
    60 nm from the center

    Gale Force Winds
    ==================
    240 nm from the center in eastern quadrant
    210 nm from the center in western quadrant

    Dvorak Intensity: T4.0

    Forecast and Intensity
    =========================
    24 HRS: 30.3N 133.0E – 70 knots (CAT 3/Strong Typhoon) 200 km east of Tanegashima (Kagoshima Prefecture)
    48 HRS: 32.8N 135.6E – 65 knots (CAT 3/Strong Typhoon) 80 km south of Shionomisaki (Wakayama Prefecture)
    72 HRS: 36.2N 143.0E – 55 knots (CAT 2/Severe Tropical Storm) Sea East of Japan (Ibaraki Prefecture)

  7. @Buzzard, You have such strong opinions on this matter! If you’re so dissatisfied with the quality of the forecasts by highly trained & experienced meteorologists, perhaps you should invest the $$$ in your own equipment and go start your own weather site.

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