Haiti weakens Ernesto

Ernesto is has been clobbering Hispanolia all morning with tropical storm force winds and torrential rains. But now, the island has bitten back. Ernesto is struggling to hold his eye together, thanks to the mountainous terrain on the southwestern peninsula of Haiti. The 1:10pm and 3pm EDT Hurricane Hunter eye reports found a surface pressure estimated at 1007 mb, a big increase from this morning's 995 mb. Moreover, the eye was substantially tilted, with the calm at the surface about 25 miles south of the calm at the 10,000 foot flight level. The plane could find maximum winds of only 35 mph during that 2-hour period, so Ernesto will probably be downgraded to a tropical storm with the 5pm advisory. The center of the storm is just south of some very mountainous terrain, and this is significantly disrupting Ernesto. The upper level outflow still looks strong, wind shear is weak, and an upper-level anticyclone (clockwise-rotating region of winds) is still in place, so Ernesto will no doubt reorganize tonight once he moves away from Haiti. However, given Ernesto's small size and the difficultly he is having with Hispanolia, there is hope that the expected 1-2 day traverse of Cuba will significantly weaken him. It may take Ernesto a day or two to regain hurricane strength once he emerges into the Florida Straits. This bodes well for the Florida Keys, which may dodge another hurricane. I think that only if Ernesto makes landfall north of Tampa will he have time to organize into a major hurricane.

The Keys evacuate
Monroe County emergency management is taking no chances, and has ordered a mandatory evacuation of all visitors and non-residents in the Florida Keys beginning at 1 pm this afternoon. A local state of emergency has been declared by Monroe County at noon today. All County and state Parks are encouraged to close this afternoon. At 10 am Monday, an evacuation for all mobile home residents will go in effect.


Figure 1. A view of the southwestern peninsula of Haiti, looking towards Cuba. Note the mountainous terrain and totally denuded of trees. Deforestation in Haiti has claimed over 99% of all the forests. The lack of forest cover to absorb Ernesto's torrential rains will cause deadly floods throughout southern Haiti today and Monday. Image credit: Google Earth.

The intensity forecast
There is no major change to the intensity forecast. As long as Ernesto is not interacting with Cuba or Hispanolia, he should strengthen. A low-shear environment with an upper-level anticyclone (clockwise rotating region of winds) has developed on top of the storm. These conditions are highly favorable for intensification. Ernesto is over waters of 30-31 C (86-88 F), and these waters warm up to nearly 90F in the narrow channel between Jamaica and Cuba. These warm waters extend to great depth, and the total heat content available to fuel rapid intensification is high. However, given the sharp decrease in intensity of Ernesto, thanks to its interaction with Hispanolia, I no longer expect Ernesto will have enough time to reorganize and attain Category 2 status for its Cuba landfall. Expect a Category 1 hurricane.

The track forecast
The 12Z (8am EDT) models are in, and continue to show Florida will get a double hit--first the Keys, then the main Peninsula. The GFDL model is the furthest west, favoring a hit in the Panhandle as a Category 3 hurricane. The GFS is the farthest east, calling for a hit on Key Largo as a tropical storm. The other models are in between. At this point, there is no reason to disqualify any of these model solutions as unreasonable. It still appears that New Orleans can breathe easy, as Ernesto should miss that city by a wide margin. However, residents of the U.S. southeast coast need to be prepared for tropical storm conditions if Ernesto crosses Florida and then re-intensifies off the Southeast coast. Several of the models indicate a track curving along the Southeast Coast just offshore, which may bring tropical storm conditions to Georgia, South Carolina, and North Carolina. Ernesto is not a threat to New England.

The storm surge forecast
Ernesto should not generate as high of storm surge in the Keys as Hurricane Wilma did last year. Storm surge heights should be four feet or less. Cuba will block the formation of the mound of storm surge water that Ernesto is piling up today and Monday, and the storm will have to generate a new mound of storm surge water once it crosses into the Florida Straits. North of the Keys, any hit along the west coast of Florida as a Category 2 or higher storm will generate a 10 foot or higher storm surge, due to the shallow waters extending out for a great distance from the coast.

Next update
The Hurricane Hunters will be in Ernesto until about 5pm EDT this afternoon. The next mission is at 8pm EDT tonight. The NOAA jet is scheduled to fly tonight as well, so we'll have our first set of higher-reliability model runs Monday morning. The NOAA P-3 gets its first action Monday morning, and will fly their SFMR instrument that measures surface winds over the entire area. I may have a short update tonight if there's a significant change to report, otherwise I'll see you in the morning.

Jeff Masters