Tropical moisture was situated over South Texas on the morning of September 28th, 2012. Additional moisture from the remnants of Hurricane Miriam in the Eastern Pacific was moving into the mountains of Mexico and streaming into South Texas. A stationary front was situated over Central Texas, as an upper level disturbance was approaching from the west, ready to impact the western portions of South Texas Friday night. The combination of very high moisture, forcing along the stationary front, the upper disturbance and upslope flow over the mountains of Mexico was an ideal set up for heavy rainfall to occur over South Texas during the late evening of September 28th through the early evening of September 29th.
Showers and thunderstorms began to develop and organize over the mountains of Mexico and the frontal boundary late Friday evening, as the upper level disturbance began to impact the area. The storms moved into the Laredo area about an hour before midnight on the 28 th, producing very heavy rainfall and widespread flooding in the city. Flooding was first reported in the city of Laredo shortly after midnight September 29th, with some locations receiving nearly 6 inches of rain in just a couple of hours. The complex of storms continued to move east, producing wind damage in portions of Live Oak County just before 300 AM CDT, and heavy rainfall elsewhere. The system weakened as it approached the coast, but still was producing heavy rains. Individual thunderstorms developed over the Gulf of Mexico producing wind gusts near 50 mph. The storms then moved east on the 29 th, giving the atmosphere time to recover for the afternoon round of convection.
By mid-afternoon on the 29th, the frontal boundary began to approach South Texas. Skies had sufficiently cleared behind the morning storms to allow the atmosphere to destabilize. This led to another round of showers and thunderstorms (some producing heavy rainfall), mainly over the eastern half of South Texas. Surface winds shifted more to the east as the boundary approached the coastal areas, helping to produce an EF-0 tornado near Port Lavaca and a waterspout east of Port Aransas late Saturday afternoon on the 29 th. The thunderstorms finally moved offshore by mid-evening, as drier air began moving into South Texas.
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON... ..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.... ..REMARKS.. 1206 AM FLASH FLOOD 3 NNW LAREDO 27.57N 99.50W 09/29/2012 WEBB TX TRAINED SPOTTER WATER OVER MINES ROAD NEAR INTERSTATE 35. 1249 AM FLASH FLOOD N LAREDO 27.53N 99.49W 09/29/2012 WEBB TX EMERGENCY MNGR STRANDED MOTORISTS AT SEVERAL LOCATIONS ON NORTH SIDE OF LAREDO. 0136 AM FLASH FLOOD LAREDO 27.53N 99.49W 09/29/2012 WEBB TX EMERGENCY MNGR NUMEROUS REPORTS OF STRANDED MOTORISTS THROUGHOUT THE CITY OF LAREDO. MANY LOW WATER CROSSINGS UNDER WATER. 0148 AM HEAVY RAIN 2 NNW LAREDO 27.57N 99.49W 09/29/2012 M4.20 INCH WEBB TX AMATEUR RADIO REPORTED 1/4 MILE EAST OF KGNS TV STUDIOS. 0157 AM HEAVY RAIN 1 N LAREDO 27.55N 99.49W 09/29/2012 M5.62 INCH WEBB TX COCORAHS MEASURED AT SALDANA AND JACAMAN RD. WIDESPREAD FLOODING ALSO REPORTED IN THE AREA. 0250 AM TSTM WND DMG THREE RIVERS 28.47N 98.18W 09/29/2012 LIVE OAK TX LAW ENFORCEMENT LARGE TREE BLOWN DOWN ON OAKVILLE ROAD IN THREE RIVERS. 0255 AM TSTM WND DMG 9 NNE THREE RIVERS 28.58N 98.11W 09/29/2012 LIVE OAK TX LAW ENFORCEMENT LARGE TREE DOWN NEAR INTERSECTION OF FM 2049 AND CR 243. 0436 AM MARINE TSTM WIND 8 SE CC NAS 27.60N 97.21W 09/29/2012 M49.00 MPH GMZ250 TX MESONET BOB HALL PIER MEASURED GUST TO 43 KNOTS AND SUSTAINED AT 35 KTS. 0453 AM MARINE TSTM WIND 3 ESE CORPUS CHRISTI 27.69N 97.25W 09/29/2012 M47.00 MPH GMZ230 TX ASOS CC NAS MEASURED 41 KT WIND GUST /47 MPH/ WITH PASSING THUNDERSTORM. 0500 PM WATER SPOUT E PORT ARANSAS 27.89N 97.01W 09/29/2012 GMZ230 TX TRAINED SPOTTER BRIEF WATERSPOUT EAST OF PORT ARANSAS. 0511 PM TORNADO 1 W PORT LAVACA 28.62N 96.64W 09/29/2012 F0 CALHOUN TX NWS STORM SURVEY AN NWS STORM SURVEY CONCLUDED AN EF-0 TORNADO BRIEFLY TOUCHED DOWN JUST WEST OF HIGHWAY 35 AT FM 3084. A TRACTOR SUPPLY STORE EXPERIENCED MINOR DAMAGE WHICH INCLUDED LOSING GUTTERS OFF THE BUILDING AND A ROOFTOP AIR CONDITIONING UNIT BEING FLIPPED. WINDS WERE ESTIMATED AT 65 MPH. 0616 PM HEAVY RAIN INGLESIDE 27.87N 97.20W 09/29/2012 E2.00 INCH SAN PATRICIO TX TRAINED SPOTTER RAINFALL OF 2-2.25 INCHES IN SHORT TIME. STANDING WATER IN YARDS AND FIELDS.