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. 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. The storms moved into the Laredo area about an hour before midnight on the 28th, producing very heavy rainfall and widespread flooding in the city. Flooding was first reported in the city of Laredo  around 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 and heavy rainfall elsewhere. The system weakened as it approached the coast. The storms then moved east on the 29th, allowing the atmosphere time to recover for the afternoon round of convection.
By mid-afternoon on the 29th, the frontal boundary approached South Texas. Skies had sufficiently cleared behind the morning storms to allow the atmosphere to destabilize. This led to another round of thunderstorms 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 29th.

Thunderstorm Wind in LIVE OAK, TEXAS
From 29-SEP-12 01:50:00 to 29-SEP-12 01:50:00 (CST-6)
Location: THREE RIVERS
Magnitude: 50.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A large tree was blown down on Oakville Road in Three Rivers.

Thunderstorm Wind in LIVE OAK, TEXAS
From 29-SEP-12 01:55:00 to 29-SEP-12 01:55:00 (CST-6)
Location: RAY PT
Magnitude: 50.00 EG
Property damage: 1.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A large tree was blown down near the intersection of Farm to Market Road 2049 and County Road 243 north of the community of Ray Point.

Funnel Cloud in CALHOUN, TEXAS
From 29-SEP-12 15:24:00 to 29-SEP-12 15:24:00 (CST-6)
Location: NORTH SEADRIFT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Law Enforcement

A funnel cloud was reported near the intersection of Highway 35 and Highway 185 near Green Lake.

Heavy Rain in WEBB, TEXAS
From 28-SEP-12 23:01:00 to 29-SEP-12 00:48:00 (CST-6)
Location: LAREDO
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Amateur Radio

Very heavy rainfall was reported, through amateur radio, to have occurred about a quarter of a mile east of the KGNS-TV studio. The spotter reported 4.2 inches of rain was measured.

Flash Flood in WEBB, TEXAS
From 28-SEP-12 23:05:00 to 28-SEP-12 23:25:00 (CST-6)
Location: LAREDO
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Spotter reported water over the road on Mines Road near Interstate 35.

Heavy Rain in WEBB, TEXAS
From 28-SEP-12 23:10:00 to 29-SEP-12 00:57:00 (CST-6)
Location: LAREDO
Property damage: 100.00K
Crop damage: 0.00K
Reported by: CoCoRaHS

A rainfall observer reported very heavy rain occurred near intersection of Saldana and Jacaman Road. The observer measured 5.62 inches of rain. Widespread flooding was reported in the area.

Flash Flood in WEBB, TEXAS
From 28-SEP-12 23:45:00 to 29-SEP-12 00:30:00 (CST-6)
Location: (LRD)LAREDO INTL ARP
Flood cause: Heavy Rain
Property damage: 100.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Rising water stranded motorists at several locations on the north side of Laredo.

Flash Flood in WEBB, TEXAS
From 29-SEP-12 00:25:00 to 29-SEP-12 00:45:00 (CST-6)
Location: LAREDO AFB
Flood cause: Heavy Rain
Property damage: 250.00K
Crop damage: 0.00K
Reported by: Emergency Manager

Numerous reports of motorists stranded in rising water throughout the city of Laredo. Many low water crossings were under water.

Tornado in CALHOUN, TEXAS
From 29-SEP-12 16:11:00 to 29-SEP-12 16:12:00 (CST-6)
Location: PORT LAVACA
Tornado F-scale: EF0
Property damage: 100.00K
Crop damage: 0.00K
Reported by: NWS Storm Survey

An NWS storm survey concluded an EF-0 tornado briefly touched down just west of Highway 35 at Farm to Market Road 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.