Tropical moisture is still expected to cause heavy rainfall across much of southern Texas and western Louisiana this weekend through early next week. The increase in moisture is due to a tropical wave in the southern Gulf of Mexico. This wave is being monitored by the National Hurricane Center (NHC) and has a 10% chance of development over the next few days (see Fig. 1). The reasoning behind there only being a 10% chance of development into a tropical cyclone is because environmental conditions are not particularly favorable for cyclogenesis and low support from numerical guidance. Wind shear has been high in the Caribbean and dry air flowing down from Mexico have hindered development. With that said, the wave is moving into an environment that is slightly more favorable for development. Environmental wind shear is more relaxed in the Gulf (see Fig. 2) and there is increased surface convergence (see Fig. 3). This has led to a flareup of convection (see Fig. 4) associated with the wave this morning. It is possible that development percentages will be slightly increased this afternoon by the NHC.
Fig. 1: NHC Forecast Graphic
Fig. 2: University of Wisconsin Wind Shear Map
Fig. 3: University of Wisconsin Surface Convergence Map
Fig. 4: Morning IR Imagery
Regardless of development into a tropical cyclone, this wave will slowly move towards the Texas Coast over the next 48 hours, increasing moisture. Isolated to scattered convection will begin to impact coastal areas of the western Gulf today with more widespread and heavier rainfall impacting this region Sunday through Tuesday. Widespread rainfall totals of 1-3″ are likely across southern Texas and southern Louisiana with 3-6″+ amounts possible for coastal Texas and southwestern Louisiana (see Fig 5). Cities that will likely see impacts from heavy rainfall are: Galveston, TX; Houston, TX; Austin, TX; San Antonio, TX; Brownsville, TX; Lake Charles, LA and Lafayette, LA.
Fig. 5: WPC Precipitation Forecast Through 7-Days
Other impacts in this region are gusty winds with thunderstorms, cloud-to-ground lightning, and coastal flooding from prolonged on-shore flow. The moisture associated with this system may move eastward by mid-week towards parts of the Mid-West potentially increasing rain chances for this region and areas east of the Mississippi beyond this timeframe. There is also the possibility this wave may stall in southern Texas/northern Mexico. These details will be ironed out with time.
Please remember to turn around don’t drown!