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Ernesto strengthening slows but continues

For a couple days now we have been talking up Ernesto and warning that there was a significant chance that this could be the new big story. After looking at the situation today, I am convinced that things could be very bad indeed. I always try not to incite undue worry, but Ernesto could get ugly. Those of you in the Gulf Coast need to re-examine your hurricane plans, especially if you live in the north Gulf from Houston to Tallahassee. A very deep layer of warm water in the northern Gulf could allow for Ernesto to become a very powerful hurricane if it reaches the area.

With the latest advisory, NHC has maintained Ernesto's wind speed at 50 mph, but the central pressure is down to 997 mb. Ernesto is slowly but steadily intensifying and satellite estimates indicate a slightly stronger storm than NHC is listing due to the effect shear has on the estimates. The official forecast calls for Ernesto to enter the Gulf of Mexico early next week, where it could become a very powerful hurricane. Tropical storm watches and warnings are now active for Jamaica and parts of Hispanola. Hurricane watches are now up for Jamaica and the Cayman Islands. Ernesto may reach hurricane strength some time in the next 24-36 hours, and NHC expects it to do so in a couple days near Jamaica. A couple days ago I was calling for Ernesto to be a hurricane by tonight, and that certainly is not out of the question if wind shear lets up.

Ernesto's limited strength thus far has been due to moderate wind shear displacing the convection from the center of circulation. While the center of circulation used to be on the very edge of the convection, it is now within the convection but displaced towards the west. This wind shear should lessen today and tomorrow, and allow for strengthening to continue. The current convective pattern is very healthy and Ernesto seems to mean business. As I will explain later, the Western Caribbean holds much deeper warm water that can allow for rapid intensification.

The models are in clear consensus on a track over the western tip of Cuba by Tuesday. By early to mid next week, Ernesto could be roaming the Gulf of Mexico as a hurricane. The GFDL model is no longer an outlier and has joined the main back. Of the models still forecasting a strike on the Yucatan, three of them are variations on the same Beta-drift and Advection Model, and even these models have been shifting north in the last couple of runs. Houston, New Orleans, Biloxi, Mobile, Pensacola, and Panama City and all now in the potential danger zone. Due to disrupting of the hurricane while it passes over and near land in Jamaica and Cuba, it will be hard to make any forecasts on a landfall point along the Gulf Coast until Ernesto clears Cuba and settles into the Gulf. This is evident in the divergence of the model tracks past Cuba.

Most of my trusted models are also calling for Ernesto to strengthen into a hurricane. The GFDL, GFDN, SHIPS, LGEM are all calling for steady intensification of Ernesto into a dangerous hurricane. The only models not calling for intensification are global models that very often have trouble with hurricanes. Accordingly, their output is not very reliable and I am ignoring it.

The ocean is ripe for Ernesto when he reaches the western Caribbean and Gulf of Mexico. Let's take these one at a time, though. Below is a map of Tropical Cyclone Heat Potential (TCHP) in the Caribbean. TCHP is basically the amount of energy in the water that is available to a tropical system. Technically it is the thermal energy above 26 degrees C in the surface layer, but for our purposes just consider it the amount of fuel available to support a hurricane. Note that the area where Ernesto has been is fairly lacking in fuel when compared to the western Caribbean near Jamaica, where Ernesto is headed.

Taking a quick look at sea surface temperatures (SSTs) in the Gulf of Mexico does not provide much insight. During the summer the Gulf becomes covered in a thin film of very warm water which hides the true nature of the water underneath. Right now you can see that very warm water across the entire Gulf of Mexico.

Knowing that warm water expands provides a powerful tool in examining the surface of the ocean. By using radar altimeters aboard satellites, we can actually see an expansion of the ocean and higher sea levels where there are deep layers of warm water. One such deep layer is positioned just south of Louisiana at this time. Oceanographers call these features "warm core rings" and they are nothing more than warm parcels of water that break off of the Loop Current near the Florida Keys and drift northward towards Louisiana and eventually westward towards Texas. This particular warm core ring is extremely strong and would provide and incredible amount of energy to any hurricane that would pass over it. Warm core rings weaker than this one were responsible of the very rapid strengthening observed in hurricanes Opal, Katrina, and Rita among others. If Ernesto were to drift over this warm tongue of water with favorable atmospheric conditions, as are currently being forecast at that time, Ernesto could undergo a very rapid strengthening. It is worth noting that a similar feature is noticeable to the south of Cuba in the previous map.

Posted by Bryan Woods | Permalink