Synopsis

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.

Summary

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.

Radar Loop from 9/28/12 700 PM CDT to 9/29/12 1000 PM CDT

Satellite Loop from 9/28/12 945 PM CDT to 9/29/12 515 AM CDT


..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.

Radar Signature at the time of the EF-0 Tornado in Port Lavaca

Roof damage caused by the EF-0 Tornado in Port Lavaca

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