Weather Nerd

Dolly may breach Rio Grande levees

Officials in Cameron County, Texas are urging residents in flood-prone areas to evacuate, as they believe Tropical Storm Dolly’s heavy rains may overwhelm the river levees along the Rio Grande:

Officials don’t believe the levees will hold up to the amounts of water Tropical Storm Dolly is expected to bring to the area.

Some parts of the levee near San Benito could experience flood levels three feet above normal.

“I ask that any residents that live near the levee in Cameron County to please move away from the river levees near the Rio Grande River. We believe those will be breached if the path continues,” said Johnny Cavazos, emergency management coordinator for the county.

Tropical Storm Dolly is taking the same [tra]jectory as Hurricane Beulah in 1967, officials said.

This jives with Eric Berger’s assessment that “the biggest concern from this storm will come from inland flooding.”

Here’s what the National Weather Service in Brownsville is saying about Dolly:

…DOLLY SOON TO BECOME A HURRICANE AND NOW ON TRACK FOR THE RIO GRANDE WITH INCREASING THREAT FOR FRESHWATER AND RIVER FLOODING…

. . . INITIAL FEEDER BANDS WILL RACE ASHORE FROM SOUTH PADRE ISLAND TO BROWNSVILLE BEFORE NOON…AND ANOTHER BAND WILL REACH INTO WILLACY AND THE REMAINDER OF CAMERON COUNTY BETWEEN NOON AND 1 PM. EACH BAND WILL INCLUDE A 15 MINUTE OF TORRENTIAL RAINS AS WELL AS BRIEF WIND GUSTS AT OR JUST BELOW 40 MPH. OTHERWISE…DOLLY IS EXPECTED TO CONTINUE STRENGTHENING TO A MINIMAL HURRICANE LATER TODAY WHILE EXPECTED TO BEGIN BENDING TO THE NORTHWEST TOWARD THE RIO GRANDE LATER TODAY…CONTINUING TONIGHT. IT IS VIRTUALLY CERTAIN FOR AT LEAST TROPICAL STORM FORCE WINDS AND HURRICANE FORCE GUSTS ACROSS THE COASTAL COMMUNITIES OF THE LOWER RIO GRANDE VALLEY LATER TONIGHT AND ESPECIALLY ON WEDNESDAY. . . .

COASTAL RESIDENTS SHOULD RUSH TO COMPLETION LAST MINUTE PREPAREDNESS AND PROTECTION. MOBILE HOME AND RECREATIONAL VEHICLE RESIDENTS ARE URGED TO EVACUATE FROM THE COASTAL ZONE DUE TO EXPECTED HURRICANE FORCE WINDS. OTHERS SHOULD COMPLETE PREPARATIONS INCLUDING BOARDING UP WINDOWS…SECURING DOORS AND GARAGE DOORS…AND CHECKING THEIR HURRICANE PREPAREDNESS KITS TO HAVE ADEQUATE SUPPLIES. AT LEAST SCATTERED POWER OUTAGES ARE EXPECTED..AND WIDESPREAD POWER OUTAGES ARE LIKELY ON WEDNESDAY. . . .

NORTH WINDS WILL INCREASE TO 15 TO 20 MPH BY MID AFTERNOON…GUSTING NEAR 40 MPH IN RAIN BANDS. WINDS MAY BRIEFLY DROP TO 10 TO 20 MPH THIS EVENING BUT WILL INCREASE TO 20 TO 30 MPH TOWARD MIDNIGHT AS ADDITIONAL RAIN BANDS HEAD INLAND. SUSTAINED TROPICAL STORM FORCE WINDS ARE LIKELY OVERNIGHT…AND BECOMING NEAR CERTAIN BY WEDNESDAY MORNING WITH HURRICANE FORCE GUSTS POSSIBLY ARRIVING BY DAYBREAK WEDNESDAY.

DANGEROUS WINDS ARE POSSIBLE!

POORLY CONSTRUCTED OR UNSECURED MOBILE HOMES MAY BE DESTROYED. OTHERS MAY RECEIVE SUBSTANTIAL DAMAGE TO ROOFS…WALLS…AND WINDOWS…AND COULD BECOME UNINHABITABLE. HOUSES OF POOR TO AVERAGE CONSTRUCTION MAY HAVE PARTIAL WALL AND ROOF FAILURE…AS WELL AS BLOWN OUT WINDOWS. MANY LANAI SCREENS AND POOL CAGES WILL HAVE DAMAGE…SOME COULD BE DESTROYED. UNSECURED LIGHT TO MODERATE WEIGHT OUTDOOR ITEMS WILL BECOME PROJECTILES…CAUSING ADDITIONAL DAMAGE AND POSSIBLE INJURY. MANY AREAS COULD HAVE POWER OUTAGES…HUNDREDS OF WIRES MAY FALL…TRANSFORMERS COULD POP…AND SOME POWER POLES MIGHT BE PULLED DOWN.

ROTTING LARGE TREES WILL BE UPROOTED…MOST COMMON ON SATURATED GROUND. NUMEROUS LARGE BRANCHES OF HEALTHY TREES WILL SNAP…AND MODERATE DAMAGE IS POSSIBLE IN CITRUS ORCHARDS. UP TO ONE HALF OF NEWLY PLANTED CROPS MAY BE DAMAGED.

Of note, high-profile vehicles have been ordered off San Padre Island as of 5:00 PM today. No other evacuations are planned.

Dolly continues to take her sweet time getting stronger. As of 2:00 PM EDT, she’s got 70 mph winds and a minimum central pressure of 990 millibars. An eyewall is beginning to form, as Dr. Jeff Masters points out, and this could portend additional strengthening, perhaps at a slightly faster rate. Exposively rapid intensification is still considered unlikely, however, and Dolly will very likely max out at Category 1 strength.

The most recent NHC discussion, as of 11:00 AM EDT, forecasts a landfall intensity of 90 mph — high-end Category 1 intensity. But Berger calls this prediction ” a highly speculative guess,” and the forecasters acknowledge that 90 mph is slightly higher than the computer models actually suggest. The NHC is trying to be cautious and predict the worst.

Also at 11:00 AM, Hurricane Warnings north of Corpus Christi were lowered to Tropical Storm Warning, reflecting the decreased likelihood of a more northerly track. That said, there is still some uncertainty about the track forecast. Dr. Masters writes:

A trough of low pressure approaching the Midwest U.S. tonight will weaken the steering currents driving Dolly west-northwest, and probably impart more of a northwesterly motion to the storm tonight and Wednesday. The exact influence this feature will have on Dolly is uncertain, with four models predicting a landfall in northeastern Mexico–the UKMET, ECMWF, NOGAPS, and GFS–and two models predicting a Texas landfall–the GFDL (near Brownsville) and the HWRF (near Corpus Christi). Dolly could come ashore anywhere within the cone of uncertainty, and one should not assume the storm will track down the “skinny black line” NHC has drawn through their official forecast. The timing of Dolly’s landfall, as predicted by the computer models, will be anywhere from 10 am – 10 pm Wednesday. However, the GFS and ECMWF hint that Dolly may stall out right by the coast Wednesday, and some slow and erratic motion is possible tomorrow before the storm finally comes ashore.

This will probably be my last full update until late tonight or early tomorrow, as I’m boarding a plane this afternoon, and then I have a long drive after it lands. However, I will try to post brief updates, possibly via cell phone, to keep you apprised of any major developments.

Meanwhile, as I said previously, you can keep abreast of the situation by checking the National Hurricane Center website, the Brownsville Herald, and the various sites linked in my blogroll at right. Also, you can follow Dolly’s progress visually on the long-range radar loop and, later, the short-range radar loop out of Brownsville, as well as the infrared satellite loop.