Key Messaging Points:
- Heavy rainfall possible east of I-35 Friday through Monday, leading to life-threatening flash flooding and river flooding.
- Average rainfall amounts of 8-12″ possible east of I-35 with isolated higher amounts in excess of 15″ south of I-10. This could lead to life-threatening flash flooding and river flooding in this area, especially given the forecast slow movement and possible stall in Harvey across South Texas. Areas along and west of I-35 could see 2-4 inches with isolated higher amounts. There is the possibility of higher amounts than this in the San Antonio area based on recent model trends.
- There remains uncertainty in the forecast track of Harvey across Texas. Only small changes to the track or forward speed of Harvey will result in large changes to impacts across South Central Texas. Much higher rainfall amounts will be possible across South Central Texas, including areas into the I-35 corridor, if the track shifts further west or if Harvey stalls or slows forward speed.
Update Since Last Briefing:
- Track guidance has been nudged farther west and forecast forward speed of Harvey over South Texas has slowed.
- Projected rainfall amounts east of I-35 and south of I-10 have increased (see below).
- A Tropical Storm Watch remains in effect for Fayette, Gonzales, Wilson, Karnes, DeWitt, and Lavaca Counties.
Threats & Impacts:
Note…a change in track and intensity may dramatically change the impacts and locations of these threats/impacts.
Rainfall: 8-12 inches of rain east of Interstate 35 with isolated totals that may exceed 15 inches south of I-10 Friday through Monday. These isolated totals are most likely to occur south of I-10 and east of I-35. Life-threatening flash flooding and river flooding is possible across this area. Areas along and west of I-35 could see 2-4 inches with isolated higher amounts. There is the possibility of higher amounts than this in the San Antonio area based on recent model trends
Winds: Tropical storm force winds of 40 to 50 mph are possible across the Tropical Storm Watch most likely on Saturday, but arriving as early as Friday afternoon. Gusts could exceed 60 mph. Areas to the west along the I-35 corridor may experience some low end tropical storm force wind gusts if bands push farther west.
Tornadoes: There may be a slight risk of tornadoes mainly along rain bands in the front right quadrant of landfall. These small tornadoes can happen day or night.
Timing and Overview:
Tropical Depression Harvey was located over the southwest Gulf of Mexico this evening. Over the next couple of days Harvey is expected to move northwest and strengthen into a strong Tropical Storm and then make landfall as a hurricane along the middle Texas coast late Friday. Many models now show Harvey stalling or moving slowly inland across South Texas. On the current forecast track, tropical storm force winds are expected to affect southeast sections of South Central Texas Saturday and have thus issued Tropical Storm Watches for this area (see County list above).
Flooding rain is expected to be the main concern with Harvey, especially given the forecast slow movement and possible stall in Harvey across South Texas. There remains uncertainty in the forecast track of Harvey across Texas. Only small changes to the track or forward speed of Harvey will result in large changes to impacts across South Central Texas. Much higher rainfall amounts and significant flooding could be possible across South Central Texas, including areas into the I-35 corridor, if the track continues to shift further northwest or if Harvey does indeed slow or stall.
As such please know that later updates may change the impact areas and threats.
At this time we urge you to remain closely aware of the changes to the forecast over the next 24-48 hours by monitoring the National Hurricane Center (www.hurricanes.gov) and your local forecast (www.weather.gov/sanantonio).