Flood Science News Storms

Hurricane Delta Updates by Hurricane Hal


October 7, 2020

Wed Oct 07 1200PM CDT

1. After making landfall as a cat-2 hurricane and tracking across the Yucatan Peninsula, Delta will emerge in the southern Gulf this afternoon. The NHC forecasts the storm to intensify to into a cat-3 hurricane with 120 mph winds in the southern Gulf.

2. Delta will continue tracking NW, before slowing down and making a turn to the N. The models have shifted west this morning, placing the Upper Texas Coast at higher risk for impacts.

3. Fortunately, increased wind shear and cooler water temps in the northern Gulf, should begin to weaken Delta within 12 hours of landfall. Water temps are cooler than normal because of two strong cold fronts that crossed the area in recent weeks.

4. Updates to the Hazard Area Likeliness (HAL) Index:

– Alexandria, LA has been added to the map.

– The HAL index will now refer to coastal flooding as “storm tide”, measured above the North American Vertical Datum of 1988 (NAVD88). These are the same units that provide the elevation of your home on most elevation certificates. The forecast water level is a combination of normal astronomical tides and storm surge.

Storm surge is the height of the water level above normal, but as I’ve traveled the Gulf Coast I realized people just care about two things: 1) What can I expect on my property? and 2) When can I expect it?

Most people don’t care how high the water is above normal….they just care if it will flood their house or not. All forecast and observed water levels will now be communicated in this system. Please let me know if you have questions.

– Substantial Wind Damage from 74 mph winds: Galveston has been upgraded to POSSIBLE and Shell Beach (New Orleans Metro) and Grand Isle have been downgraded to UNLIKELY.

– Substantial Flood Damage from a 6 foot + storm tide: Cypremort Point, LA has been upgraded to PROBABLE; Galveston and Port Arthur, TX have been upgraded to POSSIBLE; Gulfport, MS has been downgraded to UNLIKELY.

– Moderate Flood Damage from a 4 foot + storm tide: Cameron and Cypremort Point, LA have been upgraded to PROBABLE; Galveston and Port Arthur, TX have been upgraded to POSSIBLE

5. The most likely scenario forecasts Delta to become a cat-3 hurricane in the southern Gulf and then make landfall as a low-end cat-3 or high-end cat 2 hurricane in SW Louisiana. It would be the first cat-2 October landfall in Louisiana since Hurricane Hilda in 1964, or the first cat 3+ since 1893. Only two cat-2 October hurricanes have made landfall in Texas (1912 and 1949), and no cat 3+ hurricanes have yet made landfall in the Lone Star State in October.

6. We have many followers along the Upper Texas coast. For reference, here are the storm tide levels for Hurricane Laura (August) and TS Beta (September), in feet: Galveston Pier 21 (harborside): Laura: 5.1, Beta: 4.7 Tide Gauge on North Jetty (Bolivar): Laura: 5.19, Beta: 4.61Sea Isle, 15 miles S of Galveston City: Beta: 5.1The latest HAL index predicts exceedence of both 4-foot and 6-foot thresholds as POSSIBLE during Hurricane Delta, but neither are yet PROBABLE, for Galveston/ Bolivar. I will provide the next update on Hurricane Delta this evening.

— Hurricane Hal

Wed Oct 07 0900AM CDT

1. Hurricane Delta made landfall as a high-end category 2 hurricane with 110 mph winds on the Yucatan Peninsula this morning.

2. Delta will emerge into the southern Gulf of Mexico this afternoon and likely strengthen to a cat 3 or 4 hurricane in the southern Gulf over the next two days. The NHC forecast increases intensity to 130 mph over the southern Gulf.

3. Delta will likely make a turn to the right and approach the coast of South Louisiana. The earliest reasonable arrival time of tropical storm force winds along the Louisiana coast is Thursday evening, with a possible landfall on Friday afternoon.

4. Fortunately, increasing wind shear and cooler water temps in the northern Gulf should start to weaken Delta in the 12-15 hours before landfall. However, if Delta intensifies in the southern Gulf as forecasted, it could still make landfall as a high cat 2 or low cat 3 in South Louisiana.

5. The ocean has a memory, and storm surge heights correlate best with pre-landfall hurricane winds. Delta will push more storm surge than a landfalling hurricane of the same intensity that was intensifying at landfall.

6. Delta has been a small hurricane so far. Although the wind fields are forecast to expand in the Gulf, the size should still be smaller than recent Hurricane Laura. Smaller size is good news because it would push less storm surge and weaken quickly under less favorable conditions in the northern Gulf.

7. I updated the Hazard Area Likeliness (HAL) maps to show the likeliness of moderate and substantial damage. Changes since yesterday evening:

  • The probability of substantial wind damage from 74 mph+ winds is now UNLIKELY for Galveston and Jasper, TX.
  • The probability of moderate damage from 57 mph+ winds is now PROBABLE at Cypremort Point, LA, and UNLIKELY for Houston Metro and Freeport, TX.
  • The probability of moderate flood damage from 6″+ rainfall is now UNLIKELY at Cameron, LA.

See uploaded maps.

CNC is installing a Community Flood Information System in flood prone areas of South Louisiana ahead of Hurricane Delta. If you have an elevation certificate and you would be interested in participating, please reply to this post or send an email to Hurricane Hal at halneedham@cnc-resource.com.

For Hurricane Delta, we are interested to find partners in the New Iberia/ Cypremort Point area, as well as Houma/ Cocodrie. These areas do not have NOAA tide gauges, so our observations would fill a critical data gap, help improve the science, and make it possible to create community inundation maps after the storm.

—Hurricane Hal