Tropical weather analysis - August 5, 2012

By: KoritheMan , 5:31 AM GMT on August 05, 2012

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Ernesto

Tropical Storm Ernesto continues racing across the central Caribbean. As of the latest NHC advisory, the following was posted on the storm:

Wind: 60 mph, with higher gusts
Location: 15.4°N 72.7°W
Movement: WNW at 22 mph
Pressure: 1007 mb
Category: Tropical storm

Ernesto has been a humbling storm, to say the least. Defying all of my previous forecasts, the storm has failed to significantly intensify up to this point. In fact, reports from a reconnaissance aircraft suggest that Ernesto is less organized than earlier, and the National Hurricane Center admits the current intensity estimate may be generous. In hindsight, there were a couple things I perhaps didn't fully consider, but this is not the time. Officially, the center is purported to be on the northwestern edge of the convection, which consists of a circular ball of thunderstorms with little banding. However, I have my doubts as to whether Ernesto has a closed circulation at all based on recent aircraft fixes.



Figure 1. Latest infrared satellite image of Tropical Storm Ernesto. Image credit: NOAA

I can see pretty easily based on recent aircraft reports and the satellite signature that Ernesto lacks an inner core. It is possible Ernesto is pulling in drier air from South America to its south, as evidenced by recent TPW imagery from CIMSS; the fast forward motion isn't helping, either. However, when Ernesto approaches 80W, conditions should become more conducive to strengthening as the tropical cyclone finds itself beneath the hottest waters in the basin and under a light upper-level shear pattern. Assuming Ernesto retains some structural coherence, rapid intensification is still a possibility at that time. However, since we have little apparent skill in predicting the onset of these events, coupled with Ernesto's poor structure, I will not be indicating such at this time. Gradual strengthening is still forecast, but this is a low confidence forecast.

Ernesto could still become a major hurricane once it hits the untapped heat reservoir of the western Caribbean. However, I do not consider this possibility to be as likely as it was yesterday. The intensity forecast is reduced from yesterday to account for the likelihood of a landfall along the Yucatan Peninsula.

Ernesto has made the long anticipated turn to the west-northwest as it comes under a slight erosion in the subtropical ridge. The global models continue to suggest that a weakness will develop in the ridge over the next few days. Previously, I had anticipated that this weakness would be great enough to potentially turn Ernesto northward. But given the lack of strengthening of the cyclone thus far, which was not expected, this possibility is becoming increasingly less likely. Additionally, the HWRF has joined the model consensus as of 18z when it was previously forecasting a landfall along the northern Gulf Coast, which adds confidence to the forecast track.

0z upper air data over the lower 48 suggests that the trough currently moving across the northern plains is rather strong above 500 mb. As this trough moves eastward, it should weaken the ridge a bit further. By Thursday, the models suggest the arrival of another trough, this one far more potent, but Ernesto may be too far south to feel the influence of the secondary trough. The only way I can see Ernesto moving northward is from a more a poleward center reformation under the deeper convection, or it becomes a significant hurricane in the western Caribbean (Category 3 or 4). Even then, I feel that any such northward turn would occur much farther west than I was indicating yesterday. At this point I've pretty much taken areas from Louisiana eastward out of the woods given recent model trends and the relative storm organization. It is possible that the secondary trough could cause some rather slow motion prior to Ernesto's final landfall.

5-day intensity forecast

INITIAL 08/05 0300Z 50 KT 60 MPH
12 hour 08/05 1200Z 50 KT 60 MPH
24 hour 08/06 0000Z 55 KT 65 MPH
36 hour 08/06 1200Z 60 KT 70 MPH
48 hour 08/07 0000Z 65 KT 75 MPH
72 hour 08/08 0000Z 75 KT 85 MPH
96 hour 08/09 0000Z 70 KT 80 MPH...INLAND
120 hour 08/10 0000Z 75 KT 85 MPH...OVER WATER

5-day track forecast



Figure 2. My 5-day forecast track for Ernesto.

Watches and warnings

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* JAMAICA

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA WITHIN 36 HOURS.

INTERESTS IN THE CAYMAN ISLANDS AND THE YUCATAN PENINSULA OF MEXICO
SHOULD MONITOR THE PROGRESS OF ERNESTO. A TROPICAL STORM WATCH MAY
BE REQUIRED FOR PORTIONS OF THE CAYMAN ISLANDS ON SUNDAY.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.



Florence

Tropical Storm Florence continues to intensify as of the latest NHC advisory:

Wind: 60 mph, with higher gusts
Location: 16.1°N 33.0°W
Movement: WNW at 15 mph
Pressure: 1000 mb
Category: Tropical storm

Florence has changed little in organization since the advent of the most recent NHC advisory, with fairly deep convection near the low-level center.



Figure 3. Latest infrared satellite image of Tropical Storm Florence. Image credit: NOAA

Earlier microwave data indicated that the inner core structure of the tropical cyclone was well-defined. Although Florence is experiencing little vertical shear, water vapor imagery suggests that it is approaching a rather stable airmass. In addition, the SHIPS analysis of areal sea surface temperatures is at the lower end of 26C, rather cool waters for a hurricane. While a little more intensification is possible over the next 12-24 hours, in all likelihood Florence is near its peak intensity. Watch it surprise me and become a hurricane. Although the cyclone is forecast to approach warmer water temperatures on Tuesday, that will be coincident with a significant increase in westerly shear, which is expected to slowly chew away at Florence. Because Florence is a small storm, this shear could kill it off before the end of the forecast period, but I am not explicitly showing it at this time.

The track forecast is relatively straightforward. Florence is on the south side of the Bermuda-Azores ridge, which is propelling it toward the west-northwest. This general motion is expected to continue throughout the forecast period as the cyclone maintains enough vertical integrity to feel a rather large weakness in the subtropical ridge forecast to lie along 50-55W at the end of the forecast period. With slight differences in the strength of the system, the global models are in good agreement with this.

5-day intensity forecast

INITIAL 08/05 0300Z 50 KT 60 MPH
12 hour 08/05 1200Z 55 KT 65 MPH
24 hour 08/06 0000Z 55 KT 65 MPH
36 hour 08/06 1200Z 50 KT 60 MPH
48 hour 08/07 0000Z 45 KT 50 MPH
72 hour 08/08 0000Z 35 KT 40 MPH
96 hour 08/09 0000Z 25 KT 30 MPH...POST-TROP/REMNANT LOW
120 hour 08/10 0000Z...DISSIPATED

5-day track forecast



Figure 4. My 5-day track forecast for Florence.

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.