Storms

Hanna

|

July 25, 2020

Sat July 25 Evening Field Notes

Five quick facts about Hurricane Hanna after a day in the field in South Texas:

1) Hanna made landfall as a category-1 hurricane with maximum sustained winds of 90 mph, at Padre Island, Texas. The eye crossed the coast approximately 70 miles south of Corpus Christi. The wind impacts struck a sparsely populated area of South Texas so I don’t expect much wind damage to be reported.

2) Hanna was the first hurricane of the 2020 Atlantic Hurricane Season and the earliest “H” storm on record. The previous earliest “H” storm was Harvey, which formed on August 3, 2017.

3) Hanna generated the highest salt water levels near Corpus Christi since Hurricane Allen in 1980, and the 8th-highest since 1900. These data come from the U-Surge project (www.u-surge.net) which has now archived the water level of 43 hurricanes and tropical storms within 10 miles of Corpus Christi. Jeff Masters with Yale Climate Connections referenced U-Surge in his excellent post about Hurricane Hanna today. Link: https://www.yaleclimateconnections.org/2020/07/hurricane-hanna-first-atlantic-hurricane-of-2020-plows-toward-texas/

4) Slow-moving hurricanes usually inflict wind damage before flood damage. The flood game is just beginning. Water levels are still rising in Corpus Christi Bay and other bays in this region as of the time of this post. Given Hanna’s slow forward motion, heavy rain bands will likely train, especially in central and south Texas, Saturday night and Sunday. Expect localized flooding. Cannot rule out some localized pockets flooding all the way to the upper Texas coast.

5) The most substantial flooding I’ve seen so far is on the small peninsula just north of downtown Corpus Christi. Water was running 2 feet or higher in some streets…and rising. Continued heavy rain and a prolonged east wind that will keep salt water levels elevated, should combine to flood some buildings in this region Saturday night and Sunday. Several were close to flooding Saturday evening and I couldn’t see many buildings on the most flooded streets because the water was too deep to drive.

Take care everyone and stay safe!

Sat Jul 25 1PM CDT

Tracking Hurricane Hanna, the first hurricane of the 2020 Atlantic Hurricane Season, this afternoon in South Texas. As of midday Saturday, heavier rain bands moving were moving into Corpus Christi, Texas. Winds increasing but still from the north. Water levels here along the bay should start rising rapidly when winds shift from northeast then east, later this afternoon.

I haven’t seen any buildings flood yet, but I think some buildings in low-lying areas will either flood or cut it very close later this afternoon and evening. Heavy rain will not drain quickly with the persistent onshore flow keeping salt waters high. My position shows up as a blue dot on one map and the point of the red arrow on the radar map.

Fri Jul 24 11AM CDT

Tropical Storm Hanna is becoming better organized, as it continues to track to the WNW at 9 mph. Maximum sustained winds have increased to 45 mph.

Additional strengthening is forecast as Hanna tracks towards the Coastal Bend and South Texas. The National Hurricane Center (NHC) forecasts Hanna to become a strong tropical storm with maximum sustained winds of around 65 mph at landfall.

Keep up with my video updates on the CNC YouTube channel!

As Hanna is in a favorable environment for strengthening, with wind sheer (cross winds) reducing as it moves towards Texas, we should carefully monitor the forward speed. A reduction of forward speed would mean more hours over tropical waters and potentially additional strengthening.

I uploaded my first-ever “Texas-Centric” Hazard Area Likeliness (HAL) Map to this post. The map shows the likeliness of a tropical cyclone’s three main hazards: wind, rain and storm surge.

WIND
Tropical storm force winds (exceeding 39 mph) are PROBABLE for Kingsville, Corpus Christi and Rockport and POSSIBLE for areas south of Kingsville, as well as Port O’Connor, Matagorda and Freeport.

RAIN
At least 6 inches of rain is PROBABLE for Kingsville, Corpus Christi and Rockport, and POSSIBLE up the coast through Galveston, as well as locations south of Kingsville. My interpretation differs somewhat from the NHC guidance on this hazard, as they map heavier rain farther south (SPI, Brownsville, McAllen) and less rain along central and upper Texas coast. I’m adapting my forecast based on historical storms that sucked in considerable dry air near and south of the eye in this region, and offset the rain considerably to the north of landfall.

STORM SURGE
A storm surge exceeding 4 feet is POSSIBLE from Port Mansfield north through Port O’Connor. The most likely location for storm surge exceeding 4 feet are along the southern and western shores of large bays, like Corpus Christi Bay and Aransas Bay.

The NHC public forecast on storm surge provides a range of 1-3 feet along the entire Texas coast. My forecast is a bit higher than this. Given the broad circulation and relatively shallow waters of the western Gulf, I am forecasting storm surge in the 2-4 foot range for the entire Texas Coast north of Port Mansfield, with localized areas of 3-5 feet, particularly in the bays along the Coastal Bend, from localized forcing of strong winds in the bay.

Storm surge levels already reached 2 feet in Galveston this morning and most of the beach was covered with salt water. I estimate that this water level comes from a combination of long-term sea level rise since the tide gauge was last set (6-9 inches) and the influence from the northeasterly flow around Hanna (12-15 inches). We should expect multiple cycles of minor coastal flooding all the way to the Louisiana border through Saturday.

Hanna’s most severe impacts may come from “compound flooding”, where prolonged storm surge impedes the drainage of torrential rains. In other words, given the prolonged elevated salt water levels north of the circulation, rainfall will not drain as quickly as usual.

I uploaded a map showing the probability of tropical storm force winds with the arrival times from the NHC. Locations along the central Texas coast and Coastal Bend should expect tropical storm force winds to set in over night tonight.

I also uploaded a radar map from the National Weather Service, which shows outer bands of Hanna already reaching southwest Louisiana and approaching the Texas coast. Expect the first substantial rain bands to reach the Texas coast this afternoon.