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Dolly intensifying rapidly as it approaches landfall

By: Dr. Jeff Masters, 1:18 PM GMT on July 23, 2008

Hurricane Dolly is putting on a impressive burst of rapid intensification as it approaches landfall on the Texas coast near Brownsville. Reports from the Hurricane Hunters show that Dolly's pressure is dropping rapidly, down 12 mb in just five hours, to 964 mb (as of the 9:17 am EDT Hurricane Hunter eye report). Dolly's central pressure dropped 15 mb in the 18 hours previous to that, so this is an impressive sudden drop this morning. Radar imagery out of Brownsville, Texas shows an well-organized hurricane, with excellent spiral banding and a 20-mile diameter eye. Visible satellite loops show an impressive eye, excellent upper-level outflow, and good symmetry. It's a good thing Dolly does not have another 24 hours over water, or it would have become a major hurricane. It takes a while for the winds of a hurricane to respond to a rapid pressure fall, and Dolly's winds do not yet reflect the recent big drop in pressure. The peak surface winds measured by the SFMR instrument on the latest Hurricane Hunter mission were 70 knots (81 mph), at 9:17 am EDT. Dolly's winds should rise above 100 mph in the next few hours.

Figure 1. Radar image of Dolly at 6:04 am CDT, several hours before landfall. During a rapid intensification phase as Dolly neared landfall, small "mesovorticies" formed in the eyewall. In the image above, you can see that the eye is distorted by the presence of four of these small vorticies embedded in the eyewall. These vorticies are several kilometers across, and have concentrated areas of very high winds capable of doing much heavier damage than the rest of the eyewall's winds.

The intensity forecast
Dolly should keep intensifying right up until landfall, now just hours away. A Category 2 hurricane is likely at landfall. Once inland, Dolly will decay to tropical storm intensity within six hours.

Links to follow:
Brownsville, TX long range radar
Texas marine forecasts and observations
Brownsville, TX weather
Corpus Christi, TX weather

Figure 2. Evacuation zones for Category 1,2,3,4,5 hurricanes. The city of Brownsville needs to evacuate only for a Category 5 hurricane. Image credit: Texas division of emergency management.

Damage expected from Dolly
It appears portions of Dolly's eyewall will pass directly over the sister cities of Brownsville, Texas, and Matamoros, in the Mexican state of Tamaulipas. Storm surge damage will be limited, due to the fact that these cities are 20-25 miles inland from the coast (Figure 2). Dolly's expected storm surge of 4-6 feet will mostly affect uninhabited sections of Padre Island, on the right side of where the 20-mile diameter eye is coming ashore. Wind damage is the primary threat from Dolly, along with flash flooding from heavy rains. Hurricane Bret spawned two damaging tornadoes in the region in 1999, and we can expect Dolly to spawn a few tornadoes as well. I expect considerable wind damage from Dolly, exceeding $100 million.

I'll have an update this afternoon, with a look at the rest of the tropics.

Jeff Masters

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