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Dean's likely impact on the Caribbean; Super Typhoon Sepat update

By: Dr. Jeff Masters, 8:17 PM GMT on August 16, 2007

The Hurricane Hunters made their first penetration of Hurricane Dean this afternoon, and found a strong Category 1 hurricane--100 mph winds, and surface pressure of 974-979 mb. Dean is now a Category 2 hurricane. Once the winds rise to 115 mph, it will be a Category 3 storm--a major hurricane. Wind shear remains near 5 knots, and is expected to remain low for the next five days. Recent satellite loops and reports from the Hurricane Hunters show that an eye has appeared. The eye is not fully formed, and has a gap on the west side. This gap is probably due to the presence of dry air on the storm's northwest side, which is getting wrapped into the storm. This dry air will persist through at least Friday, and should act to prevent Dean from undergoing rapid intensification until it clears the Lesser Antilles Islands. Dean is steadily moistening the environment around it, and may be able to overcome the dry air on Friday and put on a burst of rapid intensification. I expect Dean will become a large and extremely dangerous major hurricane by Saturday.

Latest model runs
The latest (12Z) model runs from this morning don't show much change from yesterday's runs for the 1-3 day period, but have a wider spread for the 4-5 day period. All the models show Dean moving through the Caribbean, passing over or just south of Jamaica and the Cayman Islands on Sunday or Monday, then into the western Caribbean. At that point, the models diverge. The NOGAPS model has the southernmost solution, taking Dean into northern Belize/Southern Mexico. The GFDL takes Dean through the Yucatan Channel and northwestward, towards western Louisiana. The other models are in between, with both the HWRF and UKMET nudging their tracks more to the north, grazing the tip of the Yucatan Peninsula. The GFDL and HWRF intensity forecasts both project Dean will be a Category 5 hurricane when it nears the Yucatan Peninsula. Tonight marks the first flight of the NOAA jet, and we'll have a much more reliable set of model runs Friday morning. Hopefully, this will narrow down the uncertainty of what will happen when Dean reaches the Gulf of Mexico.

Impacts on the Caribbean
Two storms in the historical record with a similar tracks and intensities to what we might expect for Dean in the Caribbean were Hurricane Gilbert of 1988 and Hurricane Ivan of 2004. Gilbert intensified to a Category 3 hurricane as it passed south of Haiti, and made a direct hit on Jamaica, passing the entire length of the island. Gilbert then began a remarkable rapid intensification spurt as it moved over the Cayman islands into the Western Caribbean, reaching an all-time record low pressure of 888 mb before it slammed into the Yucatan Peninsula. Ivan tracked a bit further south in the Caribbean, but was also a Category 5 storm after it passed Jamaica.

Lesser Antilles Islands of Martinique, Dominica, Guadaloupe, and St. Lucia
Dean will pass through the central Lesser Antilles Islands Friday morning. Martinique and Dominica will likely receive the harshest blow, although damage may also be significant on Guadaloupe and St. Lucia. Heavy wind damage will be the primary threat on these four islands, although torrential rains of 2-7 inches may cause flash flooding problems as well. Storm surge is generally not a problem in the Lesser Antilles, since the surge tends to flow around islands surrounded by deep water.

Surrounding Lesser Antilles islands from Grenada to Antigua
These islands will experience tropical storm force winds and heavy rains, but Dean's rapid forward speed will keep these rains below four inches. Puerto Rico can expect 1-3 inches of rain from the outer rainbands of Dean, but tropical storm force winds should stay just south of the island.

The Dominican Republic
The Dominican Republic suffered four deaths from flash floods due to heavy rains along the south side of the country during Ivan's passage. The northern part of the country was relatively unaffected. Five people died from Hurricane Gilbert. I expect similar effects from Dean, which will bring bands of very heavy rain over Hispaniola, leading to isolated life-threatening flash floods on Saturday. I don't think there will be any airport closures or major impact to tourist areas. The Barahona Peninsula, which juts out to the south, will be at greatest risk.

Haiti is at major risk from heavy loss of life any time a hurricane brushes the island of Hispaniola. Hurricane Ivan did not pass close enough to the island to trigger major flash flooding, and did not kill anyone. However, thirty people died in Hurricane Gilbert. Dean will take a path similar to Gilbert's and will have a similar strength, so I expect severe flash flooding in the southern part of Haiti may cause many deaths. The airport in the capital of Port-au-Prince will likely close for a time Saturday and Sunday.

If you have travel plans to go to Jamaica, plan on spending a lot of time praying for the hurricane to miss, because that is what the locals will be doing. This seemed to be what spared Jamaica in 2004, when Hurricane Ivan made a beeline for the island, then suddenly turned and wobbled around the island. Ivan still killed 17 people in Jamaica and left 18,000 people homeless. Most of the major resorts and hotels fared well, and reopened a few days after Ivan passed. Damage on Jamaica totaled $360 million. Jamaica did not fare as well in Hurricane Gilbert, which made a direct hit as a Category 3 hurricane, killing 45. Gilbert dumped up to 27 inches of rain in the mountainous areas of Jamaica, causing severe flash flooding. Gilbert was the worst hurricane to hit Jamaica since Hurricane Charlie in 1951. Gilbert left $4 billion dollars in damage, and it was difficult to leave the island for over a week due to blocked roads and closed airports. If Dean makes a direct hit on Jamaica, expect to be stranded on the island for many days, with no power. If Dean makes a close pass but misses, as is more likely, expect a few days of hassle. All Jamaica airports will likely close on Sunday when Dean will begin to batter the island.

Cayman Islands
The poor Caymans got drilled by Ivan at Category 5 strength, and have still not fully recovered. However, the islands did a great job protecting the people there, and only suffered two deaths. 95% percent of the homes and other buildings (which generally follow South Florida's building codes) were damaged or destroyed. Expect Dean to perform a similar feat if it makes a direct hit as a Category 5. If Dean passes close but misses, the islands will fare much better--Gilbert passed 30 miles to the south of the Cayman Islands, and didn't kill anyone. There was very severe damage to crops, trees, and homes, but nothing near the level of the destruction wrought by Ivan.

Cancun and Cozumel
Mexico's Yucatan Peninsula got hammered by Gilbert, which hit as a Category 5 storm with 160 mph winds and a 15-20 foot storm surge. Ivan passed to the east of the area, largely sparing it. It's a little too early to speculate on what Dean might do, but I expect the Cancun and Cozumel airports will close on Monday. This will not be a repeat of Wilma, which hung around the Yucatan for three days. Dean is a fast moving storm that will bring about a day of bad weather to the affected locations. I'll talk more about Dean's likely impact on Mexico in a later blog. If you have plans to be in Cancun or Cozumel Monday, be prepared to endure a major hurricane.

Super Typhoon Sepat
In the Western Pacific, residents of Taiwan are anxiously watching Super Typhoon Sepat, which is expected to hit the island as Category 4 or 5 storm this weekend. Wunderground meteorologist Elaine Yang, who is from Taiwan, dug up this information for me: The last time Taiwan was hit by a super typhoon was back in 2005 when Category 4 typhoon Longwang (Dragon King in Chinese) made landfall at 0515 local time on October 2nd, just south of Hualien City. Over the last 13 years, there were two typhoons, July 1994 Tim and August 2000 Super Typhoon Bilis that had similar tracks to Sepat.

South and southeast of Taiwan are under the first level of alerts. The residents have been preparing for the arrival of Sepat. Retailer stores are taking down the advertisement boards, residents are nailing their windows, and farmers are in a hurry to harvest agriculture products. The tall trees over the major roads are being cut.

Links to watch:
Martinique current conditions.
St. Lucia current conditions.
Dominica current conditions.
Guadaloupe current conditions.
Martinique radar.

I'll have an update Friday morning.

Jeff Masters

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

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