| Above: Visible satellite image of 91L taken at 9:20 am EDT June 4, 2019. Image credit: NOAA/RAMMB. |
Tropical disturbance 91L in the southern Gulf of Mexico’s Bay of Campeche remains disorganized and is running out of time to develop into a tropical depression as it heads northwest at 10 mph towards the northeast Mexico/Texas border region. However, the system has the potential to be a heavy rainmaker for the coasts of Texas and Louisiana this week.
Satellite images on Tuesday showed that 91L had a moderate-sized area of disorganized heavy thunderstorms. The system was under high wind shear of 20 knots, was over warm waters of 28.5°C (83°F) and was embedded in a moist atmosphere with a mid-level relative humidity of 75%. These conditions are marginal for development, and 91L’s large size has also been hindering development. An Air Force hurricane hunter aircraft that was scheduled to investigate 91L on Tuesday afternoon was cancelled, and no other flights are planned into 91L.
 |
| Figure 1. Radar from Brownsville, Texas at 9:41 am EDT June 4, 2019, showed a surface swirl of rains associated with 91L moving inland near the Texas/Mexico border. |
Forecast for 91L: a heavy rain threat
The 12Z Tuesday run of the SHIPS model for 91L predicted that wind shear would increase to very high levels, over 25 knots, by Tuesday night and beyond. This high shear will make it difficult for 91L to develop. In addition, the center of 91L will be very near the coast of northern Mexico and possibly move inland on Tuesday night, and this interaction with land will limit the chances for development. The 8 am EDT Tuesday 5-Day Tropical Weather Outlook from NHC gave 91L 2-day and 5-day odds of development of 40%. The next name on the Atlantic list of storms for 2019 is Barry.
A trough of low pressure that was over the Southwest U.S. on Tuesday morning will move west this week, and the southerly flow of wind in advance of this trough will force 91L to take on a more northerly track then north-northeasterly track at about 10 mph on Wednesday and Thursday. This motion will keep the center of the storm very close to or just inland along the coast of Texas and bring 91L into Louisiana by Thursday.
Tropical moisture from a broad area of low pressure in the southwest Gulf of Mexico will begin to spread northward today. Heavy rain and flash flooding will become a concern across southeast Texas and the Lower Mississippi Valley through Friday. https://t.co/bcmbaq8fLQ pic.twitter.com/RDTYjkwlNc
— NWS WPC (@NWSWPC) June 4, 2019
Even if 91L does not develop into a tropical depression, it will bring very heavy rains to the coasts of Texas and Louisiana through Thursday. The National Weather Service has issued a flash flood watch for a part of the upper Texas coast, including Houston, through Thursday morning. Rainfall amounts of 2 – 3” per hour will be possible in some of the heaviest bands, with total accumulations in excess of 6” possible in some locations. Additional flash flood watches will likely be required for other parts of the coast later in the week.
