Ernesto Almost a Hurricane

After Tropical Storm Ernesto went through a bout of rapid organization this morning, the intensity of the system has leveled off. As of the recent 5pm EDT advisory issued by the NHC, Ernesto was listed at:

Location: 16.2N 81.6W

Winds: 65 mph

Pressure: 995mb

Movement: WNW (295) degrees at 12 mph

The burst of intensification seen this morning was quite impressive. At one point during a recon center fix, the pressure dropped to 994mb and a 6-10nm eye was reported. It is quite rare for a storm of 55 knot intensity to have a closed eyewall, especially that small. Storms with small eyewalls are generally unstable, and I believe Ernesto was not able to maintain his small eyewall, which led to the leveling off in intensity. Over the past few hours convection in the core of the storm has weakened as seen by the warming cloud top temperatures. However, convection in the feeder bands around the core of the storm remains quite vigorous at this time. This is probably attributed to the downdraft generated by the collapsed eyewall which shot radially outwards from the center of the storm and helped surface convergence in the bands. The lastest IR image shows this well:

IR satellite image of TS Ernesto

Notice the brighter colors, representing colder cloud top temps, in the outer bands of the storm. Ernesto still has a great cloud pattern signature and recon consistently remarked of a great radar signature earlier as well. It is probable that later tonight, Ernesto will once again fire off a burst of convection as more air is brought back into the core of the storm. This process will be aided by diurnal maximum in the overnight hours, which favors convective development.

In terms of Ernesto’s environment, conditions are very favorable. Wind shear is a low 5-10 knots over the storm due to an upper level anticyclone just to the west of Ernesto’s center:
Wind shear analysis from CIMSS

There is also an upper level low just to the north of Hispaniola that is providing an excellent outflow channel to the NE of the storm. Outflow is pretty good in the remaining quadrants as well. Ernesto is also in a decently moist environment, especially when compared to previous days, so dry air shouldn’t be much of a problem.

Another positive factor Ernesto has going for him is very warm waters. Not only is the sea surface warm, but these warm waters extend down to a great depth. One way of measuring this is through analyzing Tropical Cyclone Heat Potential (TCHP). It is important for warm waters to extend down a great depth for stronger systems, since higher wind speeds mix up waters from below the surface. If the warm water isn’t deep enough the cyclone will upwell cool waters leading to weakening. Here is the latest TCHP analysis for the Caribbean:
Caribbean TCHP

The Western Caribbean is annually home to the highest levels of TCHP in the Atlantic Basin. TCHP values over 80 kJ/cm^2 are favorable for rapid intensification. Ernesto is forecast to miss the absurd values of over 140 as seen in the white colors, but still will move over TCHP values above 80, so rapid intensification is still a very real possibility. In fact, the 18Z SHIPS, a commonly used statistical intensity model, forecasts a 40% chance of 25 knot or greater increase in wind speed in the next 24 hours, which is 3.1 times to normal %. The SHIPS is also forecasting a 5.1 times greater than average % of a 40 knot increase in wind speed over the next 24 hours.

Personally, I think Ernesto will be about an 85 knot hurricane when he comes ashore the Yucatan Peninsula, compared to the NHC’s 75 knots. I do not want to speculate on the strength of a second landfall at this time since it will depend a lot on how much land the storm moves over.

I want to start off the track forecast by showing the current steering currents:

Ernesto Steering Currents

Ernesto is being steered by a large ridge of high pressure to its NE. There is a slight weakness between this ridge and another located over Western Texas, as seen above. Earlier, some of the models were forecasting Ernesto to strengthen quick enough to “feel” this weakness and turn into the Northern Gulf of Mexico. However, since Ernesto remains a tropical storm, this possibility is becoming increasingly unlikely, and none of the reliable computer models are still forecasting this.

Now there is a strong consensus Ernesto will move ashore the Yucatan Peninsula in the overnight hours Tuesday Night/Wednesday Morning roughly around the area of the Northern Belize/Mexico border. This morning and afternoon while recon was still in the storm, Ernesto gained quite a bit of latitude with an almost due NW movement. However, I do not think this is representative of a long-scale movement and Ernesto should bend back to the WNW tonight as the narrow ridge to the north of the system remains just strong enough to keep Ernesto headed towards the Yucatan and into the Bay of Campeche. I see no reason to disagree with the NHC’s 5pm EDT forecast track:

Forecast Track for Ernesto

Residents in the Yucatan Peninsula should be finishing up preparations as soon as possible, especially those who already under a hurricane warning. Stay tuned to the NHC for further updates as they are the sole authority for hurricanes in the Atlantic Basin. Canefever.com has info and links to help you prepare for a storm if you need any help, but these preparations need to be completed quickly.

I will have an update again when conditions warrant.

-Mike

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