Hurricane Dolly closes in on Texas/Mexico

Hurricane Dolly has become the second hurricane of the 2008 hurricane season. Dolly is barely a hurricane, and is still struggling to build a complete eyewall. Visible satellite loops show an eye developing, and heavy thunderstorm activity continues to increase near the core of the storm. Dolly has good upper-level outflow to the west and north, but restricted on the south side, where an upper level low pressure system is still interfering. Maximum surface winds measured by the SFMR instrument on the current Hurricane Hunter aircraft inside Dolly were 74 mph (65 kt), measured at 4:17 pm EDT. Brownsville, Texas long-range radar shows the eyewall is complete on Dolly's west side, but is struggling to get established on the east side. Radar estimated rainfall amounts of 1/10 of an inch have fallen on the Texas/Mexico coast so far, thanks to the outermost spiral bands of Dolly.


Figure 1. Latest long-range radar image from Brownsville, Texas.

The intensity forecast
The intensification potential for Dolly remains high, but until Dolly can form a full eyewall, it won't be able to take full advantage of the favorable environment. Wind shear over Dolly is about five knots, and is expected to remain below ten knots over the next two days. An upper level high pressure system is moving into place over the storm, which should enhance Dolly's upper-level outflow and allow more rapid intensification. Dolly is over waters of 29°C. The waters cool to about 28°C by midnight tonight as Dolly approaches the coast and passes over a cool ocean eddy. The depth of the warm waters Dolly is over has decreased, and the Tropical Cyclone Heat Potential has fallen from about 40 to 20 kJ/cm**2. This decreases the potential of rapid intensification. Our skill in making intensity forecasts is poor, but it currently appears that Dolly only has enough time to intensify into a Category 1 hurricane. A Category 2 hurricane still a possibility, though. I put the chances of Dolly reaching major hurricane status (Category 3 or higher) at 1%.

The track forecast
The track forecast has changed little since this morning, with the various computer models predicting pretty much the same behavior as they did 12 hours ago. Four models are predicting a landfall in northeastern Mexico--the UKMET, ECMWF, NOGAPS, and GFS--and two models are predicting a Texas landfall--the GFDL (just north of 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 8 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.

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

Damage expected from Dolly
I posed the question in this morning's blog, Since hurricanes began getting names in 1950, only one major hurricane that hit the U.S. did not get its name retired. Which one was it? A hint: the track was similar to Dolly's expected track. The answer is, Hurricane Bret, which hit Padre Island National Seashore, just north of Brownsville, Texas, as a Category 3 hurricane on August 22, 1999. The park is a long barrier island with few structures and no commercial developments, and the fury of Bret's 115 mph winds were confined to desolate unpopulated seashore. Bret did $60 million in damage, mostly in the small towns just inland from the National Seashore. Bret dumped 14 inches of rain on northern Mexico, and brought an 8-10 foot storm surge to Padre Island. Several new channels were cut through the barrier island, connecting the ocean to the Laguna Madre sound behind Padre Island.


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.

If Dolly follows a similar path, we can expect relatively minor damage. Even if Dolly makes a direct hit on the sister cities of Brownsville, Texas, and Matamoros, in the Mexican state of Tamaulipas, 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 probably not do much damage, since there are few structures near the coast in the region. Wind damage will be the primary threat from Dolly, along with flash flooding from heavy rains. Hurricane Bret spawned two damaging tornadoes in 1999, and we can expect Dolly to spawn a few tornadoes as well.

I'll have an update in the morning.
Jeff Masters