Hurricane Dolly (US)

Landfall | Summary
Posting Date: July 23, 2008, 11:46:00 AM

AIR estimates that losses in the U.S. from Hurricane Dolly are between $300 million and $1.2 billion with an expected (mean) loss of $600 million. The considerable uncertainty in the loss estimates is due to Dolly's slow forward motion, its significant precipitation and its future track as it makes its way inland. (In this part of the coast, a ten mile difference north or south has considerable impact on losses.) Also highly uncertain is the rate at which Dolly will dissipate over land. AIR estimates insured losses in Mexico will be less than a quarter of U.S. insured losses. However, it is important to note that the uncertainty in losses is even greater here because of the uncertainty surrounding take-up rates—that is, the percentage of properties actually insured against wind and flood losses. After slowing for several hours to a near standstill about 35 miles offshore, the eyewall of Hurricane Dolly finally crossed South Padre Island at around 1:00 pm EDT as a Category 2 hurricane with winds of 100 mph. As of 2:00 pm EDT, Dolly is located over Laguna Madre, about 35 miles north-northeast of Brownsville. Winds have diminished to 95 mph and Dolly is now a Category 1 hurricane. Central pressure is estimated at 967 mb. The National Hurricane Center reports that hurricane-force winds extend 25 miles outward from the eye, while tropical storm force winds extend out to 140 miles, lashing a broad swath of the coast near the Texas/Mexico border with strong winds and heavy rain. Forward motion is to the north-northwest at seven miles per hour. Dolly is expected to bring as much as 15 to 20 inches of rain to isolated pockets and a four to six-foot storm surge. At Category 2 wind speeds (1-minute sustained winds of 96-110 mph), many homes are likely to suffer damage to roof shingles and wall coverings. There may be also damage to unprotected windows from the wind-borne debris. On South Padre Island, the roof of an apartment complex on the island partially collapsed, although the extent of the damage is not yet known. As Dolly moved closer to the mainland, its winds knocked over signs and ripped off awnings. Power has been disrupted to an estimated 27,000 customers in Cameron County, where Brownsville is located. Exacerbating the potential damage, Hurricane Dolly virtually crawled toward Texas, battering coastal properties on both sides of the border with tropical storm and hurricane force winds long before the center of the storm actually crossed the coastline. Mitigating the damage is the fact that the sister cities of Brownsville and Matamoros--the largest exposure concentrations on Dolly's path--are located about 20-25 miles inland. In Mexico, wooden shacks in fishing communities like Higuerilla may not be able to withstand Dolly's onslaught. Neither are they likely to be insured. The dominant construction type of insured properties in Mexico is confined masonry, which should fare reasonable well. Given Dolly's slow forward speed, precipitation-induced flood damage may be significant. Dolly made an earlier landfall as a tropical storm on Mexico's Yucatan peninsula on Monday, July 21, just south of Cancun, where it caused minimal damage. Meanwhile, according to the Minerals Management Service (MMS) of the U.S. Department of the Interior, oil and gas producers in the Gulf of Mexico shut down about 5 percent of production in the Gulf by Tuesday. Personnel had been evacuated from 49 production platforms. However, Dolly's track is well south of the heaviest concentrations of offshore assets and no lasting shutdowns are expected. Physical damage to platforms and rigs is likely to be quite limited, with any insured losses dominated by business interruption. The figure below shows the AIR modeled windfield for sustained winds of 60 mph and greater overlaid on a map of rig and platform locations.

AIR modeled offshore wind speeds and platform locations. (Source: AIR)

Dolly, which spent most of its lifetime as a tropical storm, did eventually reach hurricane strength as forecast by NHC, less than a day before arriving on the Gulf coast. Sea surface temperatures (SSTs) are a key fuel source for tropical cyclones. The map below shows the temperature of the surface of the Gulf waters in the region where Dolly formed and later intensified. Note the swath of warmest Gulf temperatures (exceeding 29C) extending from the Louisiana coast through to the central Gulf and western Caribbean. Dolly's track, guided by large-scale atmospheric steering currents, took the storm over the western edge of this warm eddy.

Dolly's track and intensity overlaid on sea-surface temperatures in the Gulf of Mexico. (Source: NOAA/AIR)

During its initial development stage, before striking the Yucatan Peninsula, these warm ocean temperatures provided a favorable environment for development, but the winds did not respond to the warm waters in a dramatic way, maintaining modest wind speeds of around 40 knots, just around tropical storm strength. Dolly was then subjected to a less favorable environment, first passing over the Yucatan, then reemerging over cooler waters in the southern Gulf. Dolly then approached the southern flank of the warm water pool, and in this case intensified relatively quickly reaching hurricane strength, and eventually Category 2 strength, very close to the Texas coastline. There are three reasons why this second passage over warmer waters had more influence on Dolly's intensity: (a) the storm was moving more slowly and thus had much more time to take advantage of the latent energy stored in the warm waters, (b) the wind shear conditions in this part of the Gulf were more conducive to intensification, and (c) hurricanes are able to more efficiently convert heat energy from the ocean to wind energy than weaker tropical storms. The experience with Dolly demonstrates that under slightly different environmental conditions, and in particular under a slightly different track, the intensification cycle of such a storm could have been very different. A more southerly track may have resulted in the storm's inability to reach hurricane strength, while a more northerly track could have produced a much stronger storm. The AIR tropical cyclone team has developed scenarios for Hurricane Dolly using the latest information about the storm's current and forecast meteorological parameters, as well as its forecast track. Eleven of these are now posted on the Scenarios page of this website. Also included on the Scenarios page is AIR's probability of loss exceedance curve for the industry. Note that the loss estimates provided in this posting include wind losses to U.S. onshore properties only. AIR will post loss estimates separately for Mexico. ALERT subscribers will receive notification tomorrow when they are available. Users should be aware of a recently identified CATRADER© issue that impacts use of the "All simulated scenarios" event set in CATRADER. The issue does not affect the "Select simulated scenarios" event set of 11 scenarios. While CLFs are not compatible with ALERT event sets , the "All simulated scenarios" event set is improperly associating losses from some CLFs for programs set to "Use CLF only" or "Use CLF +sums insured" with Dolly scenarios. Until the issue is resolved, when running the "All simulated scenarios" event set in CATRADER, AIR recommends setting the Mkt. Shares drop down on the CATRADER analysis screen to "Based on sums insured." This analysis option will override the individual program settings. Please contact AIR Client Services if you have questions related to this issue.

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Posting Date: July 23, 2008, 11:46:00 AM