Tropical weather analysis - May 27, 2012
Subtropical Storm Beryl continues moving toward the southeast United States. As of the latest NHC advisory, the following was posted on the storm:
Wind: 50 mph, with higher gusts
Location: 30.8°N 77.9°W
Movement: WSW at 7 mph
Pressure: 998 mb
Category: Subtropical storm (Saffir-Simpson Hurricane Scale)
Beryl has not shown any signs of acquiring tropical characteristics thus far, with the exhibited cloud pattern still very reminiscent of a subtropical storm. However, recent satellite pictures show a stronger, more persistent convective pattern.
Figure 1. Latest infrared satellite image of Subtropical Storm Beryl, courtesy of NOAA's Satellite Services Division (SSD).
It is uncertain whether this heralds the onset of a warm core, or if it's just a fluke. CIMSS 200 mb vorticity analysis suggests that the upper-tropospheric cold low that was following Beryl has moved to the south, closer to the Bahamas, but this is not supported by water vapor imagery. Regardless, it is still anticipated that Beryl will become tropical sometime before landfall. Nearby buoy observations indicate that Beryl is traversing sea surface temperatures between 26°C and 27°C. These values are just warm enough to support a tropical storm, and with the upcoming diurnal convective maximum period, we may see Beryl try to pull off one final accolade. Another factor supporting a warm core transition is the recent contraction of the wind field; currently, tropical storm force winds extend out to only about 90 miles from the low-level center. This is in sharp contrast to this time yesterday, when they were about 25% larger.
Interestingly, the GFS forecasts about 20 kt of northerly upper-level flow to develop over Beryl today, and persist until landfall. There are no clear cut indications of that happening at this time, and I am uncertain whether this shear is related to the storm itself, or to the central United States ridge, which is forecast to slide eastward today. Lacking any large scale features to induce this shear, the ridge seems highly suspect. The only other factor I could conceivably see generating that kind of shear is for the upper low Beryl is sitting under to back out from underneath the surface low and move southeast. That is not happening at this time. In deference to this shear, I will hold off on intensifying Beryl.
5-day intensity forecast
INITIAL 05/27 0300Z 45 KT 50 MPH
12 hour 05/27 1200Z 45 KT 50 MPH...TROPICAL
24 hour 05/28 0000Z 45 KT 50 MPH...INLAND
36 hour 05/28 1200Z 35 KT 40 MPH...INLAND
48 hour 05/29 0000Z 30 KT 35 MPH...INLAND
72 hour 05/30 0000Z 30 KT 35 MPH...OVER WATER
96 hour 05/31 0000Z 40 KT 45 MPH
120 hour 06/01 0000Z 45 KT 50 MPH...EXTRATROPICAL
The type of strengthening shown after the system emerges into the Atlantic is still not certain. Whether Beryl intensifies tropically or baroclinically on Wednesday more than likely depends on the sharpness and location of recurvature. The ECMWF is farther north, which places Beryl closer to the cooler shelf waters off the southeast coast, and also closer to a large belt of westerly shear forecast to develop over the western Atlantic at that time. The models which are farther south suggest Beryl will cling to tropical characteristics a little longer, and possibly reintensify as a tropical cyclone. The models are unanimous, however, that the cyclone will lose tropical characteristics on Thursday, as a large upper-level trough and attendant cold front encroach on it from the west.
Anyway, I tend to side with the southern solution, as Beryl isn't expected to strengthen much.
5-day forecast track
Figure 2. My 5-day forecast track for Beryl.
Notice my track is a fair bit south of the National Hurricane Center's after landfall, but gradually comes into better agreement.
Tropical storm force winds are forecast to begin affecting the southeastern United States coast today. Already, coastal reports indicate winds of about 20 to 25 mph lie just offshore the South Carolina coast. These winds will gradually spread westward and onto the coast with time. Beryl may also produce isolated tornadoes and heavy rainfall.
Watches and warnings
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* VOLUSIA/BREVARD COUNTY LINE FLORIDA TO EDISTO BEACH SOUTH CAROLINA
FOR STORM INFORMATION SPECIFIC TO YOUR AREA IN THE UNITED STATES...
INCLUDING POSSIBLE INLAND WATCHES AND WARNINGS...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR LOCAL NATIONAL WEATHER SERVICE FORECAST
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