Basement-dwelling pseudo-otaku with a thrill for forecasting on the side.
By: KoritheMan , 6:22 AM GMT on July 10, 2013
Tropical Storm Chantal continues to race across the central Caribbean Sea. As of the latest NHC advisory, the following information was available on the storm:
Wind: 50 mph, with higher gusts
Location: 15.5°N 68.0°W
Movement: W at 30 mph
Pressure: 1011 mb
I am faced with a disorganized storm this evening; actually, most likely a sharp tropical wave. While the earlier reconnaissance mission into the tropical cyclone was cut short due to the crew entering Venezuelan airspace, a slew of scatterometer, satellite, and radar fixes strongly suggest that Chantal has lost its closed surface circulation. Another reconnaissance plane is investigating Chantal now, and I imagine they will find an open wave.
Figure 1. Latest infrared satellite image of Tropical Storm Chantal. Image credit: NOAA's Satellite Services Division (SSD).
Most of the deep convection has collapsed, become fragmented, and displaced well to the east of the low-level center. This is likely due to a combination of increasing westerly shear south of a well-defined upper flow off the southern Florida coast, dry air (as seen by arc clouds emanating westward from the cyclone center on satellite), and low-level speed shear. While Chantal has made some comebacks before, a rebound looks less likely this time.
Even if Chantal somehow survives the current hostilities, the 0z GFS and CMC far farther south and take it across the southwestern peninsula of Haiti; the current westward motion in excess of 25 kt may be evidence of a track farther to the south. Haiti is even more mountainous than the Dominican Republic, so that would pretty much be worst case scenario for Chantal. Even if Chantal decides to traverse the less mountainous areas of Hispaniola, a tight circulation with little to no west winds isn't going to last very long. For now, my forecast will maintain some continuity and still take Chantal over the northern portion of Hispaniola, although I have shifted a little to the left in deference to the GFS forecast.
The models show upper-level winds improving over the Bahamas as an upper low develops over the northeastern United States and retrogrades westward, providing a diffluent upper-level environment; however, Chantal will probably not last that long.
In the meantime, the models shear westerly shear increasing even further while the storm traverses Hispaniola, which is not a good sign for Chantal clinging to life.
Chantal remains south of an unseasonably strong mid-level ridge, which is responsible for the rather brisk aclimatological westward motion. Recent satellite fixes would tend to confirm the National Hurricane Center's recent assignment of a more westward component of motion. The global models show the upper low over the Florida Straits moving southward and weakening, which is expected to create a weakness in the western extent of the subtropical ridge and allow Chantal to slow down over the Bahamas. This low is forecast to gradually weaken and ultimately dissipate in a few days, while any residual troughing over the southeastern United States lifts out. With developing mid-level ridging to the north, Chantal is forecast to turn westward near the end of the forecast period, likely into the southeastern United States coast. Once again, this assumes Chantal will survive, but I do not consider this to be particularly likely in light of current trends. The sharp westward turn into the Gulf of Mexico since yesterday is no longer evident, and even if the models do somehow shift west, there will likely be very little left of Chantal to regenerate in an otherwise favorable environment in the Gulf of Mexico. The models are more tightly clustered around a Georgia/South Carolina landfall now, and my forecast will consequently be nudged in that direction as well, showing the center of Chantal just offshore the Georgia coast on Sunday evening.
It should be noted that, even if Chantal loses its status as a tropical cyclone, locally heavy rainfall and strong gusty winds, possibly in exceeding 50 kt, will be possible in squalls across Hispaniola today (Wednesday). The system is likely to also still carry winds to tropical storm force as it traverses eastern Cuba and the Bahamas.
5-day intensity and position
INITIAL 07/10 0600Z 15.5N 68.0W 45 KT 50 MPH
12 hour 07/10 1200Z 17.0N 70.0W 45 KT 50 MPH
24 hour 07/11 0000Z 18.4N 71.8W 45 KT 50 MPH...INLAND OVER HISPANIOLA
36 hour 07/11 1200Z 20.9N 74.6W 40 KT 45 MPH...OVER WATER
48 hour 07/12 0000Z 23.2N 76.5W 40 KT 45 MPH
72 hour 07/13 0000Z 27.3N 78.8W 40 KT 45 MPH
96 hour 07/14 0000Z 29.3N 79.7W 45 KT 50 MPH
120 hour 07/15 0000Z 30.7N 81.4W 45 KT 50 MPH
5-day track forecast
Figure 2. My 5-day forecast track for Chantal.
NHC storm information
WTNT33 KNHC 100547
TROPICAL STORM CHANTAL INTERMEDIATE ADVISORY NUMBER 9A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL032013
200 AM AST WED JUL 10 2013
...CHANTAL BECOMING DISORGANIZED WHILE IT PASSES TO THE SOUTHWEST OF
SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
ABOUT 235 MI...380 KM SSW OF SAN JUAN PUERTO RICO
ABOUT 230 MI...370 KM SSE OF SANTO DOMINGO DOMINICAN REPUBLIC
MAXIMUM SUSTAINED WINDS...50 MPH...85 KM/H
PRESENT MOVEMENT...W OR 280 DEGREES AT 30 MPH...48 KM/H
MINIMUM CENTRAL PRESSURE...1011 MB...29.85 INCHES
WATCHES AND WARNINGS
CHANGES WITH THIS ADVISORY...
THE GOVERNMENT OF THE DOMINICAN REPUBLIC HAS DISCONTINUED THE
HURRICANE WATCH FROM BARAHONA TO SAMANA.
SUMMARY OF WATCHES AND WARNINGS IN EFFECT...
A TROPICAL STORM WARNING IS IN EFFECT FOR...
* PUERTO RICO
* ENTIRE COAST OF THE DOMINICAN REPUBLIC
* ENTIRE COAST OF HAITI
* TURKS AND CAICOS
* SOUTHEASTERN BAHAMAS
A TROPICAL STORM WATCH IS IN EFFECT FOR...
* U.S. VIRGIN ISLANDS
* VIEQUES AND CULEBRA
* CENTRAL BAHAMAS
INTERESTS IN EASTERN CUBA AND THE NORTHWESTERN BAHAMAS SHOULD
MONITOR THE PROGRESS OF CHANTAL.
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 OFFICE. FOR STORM INFORMATION SPECIFIC TO YOUR AREA
OUTSIDE THE UNITED STATES...PLEASE MONITOR PRODUCTS ISSUED BY YOUR
NATIONAL METEOROLOGICAL SERVICE.
DISCUSSION AND 48-HOUR OUTLOOK
REPORTS FROM AN AIR FORCE HURRICANE HUNTER AIRCRAFT AND SATELLITE
IMAGES INDICATE THAT CHANTAL IS LOSING ORGANIZATION.
AT 200 AM AST...0600 UTC...THE CENTER OF TROPICAL STORM CHANTAL WAS
ESTIMATED NEAR LATITUDE 15.5 NORTH...LONGITUDE 68.0 WEST. CHANTAL
HAS MOVED RAPIDLY WESTWARD NEAR 30 MPH...48 KM/H OVER THE PAST FEW
HOURS...AND A WEST-NORTHWESTWARD MOTION WITH A GRADUAL DECREASE IN
FORWARD SPEED IS EXPECTED TODAY. A TURN TOWARD THE NORTHWEST IS
EXPECTED BY THURSDAY. ON THE FORECAST TRACK...THE CENTER OF
CHANTAL IS EXPECTED TO BE NEAR OR OVER HISPANIOLA BY THIS
AFTERNOON. CHANTAL IS EXPECTED TO BE NEAR EASTERN CUBA EARLY
THURSDAY AND OVER THE SOUTHEASTERN OR CENTRAL BAHAMAS LATER ON
MAXIMUM SUSTAINED WINDS HAVE DECREASED TO NEAR 50 MPH...85
KM/H...WITH HIGHER GUSTS. LITTLE CHANGE IN STRENGTH IS EXPECTED
BEFORE CHANTAL REACHES HISPANIOLA...BUT WEAKENING IS FORECAST AFTER
TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 90 MILES...150 KM...
MAINLY TO THE NORTH OF THE CENTER.
THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1011 MB...29.85 INCHES.
HAZARDS AFFECTING LAND
WIND...TROPICAL STORM CONDITIONS COULD OCCUR ACROSS PORTIONS OF
PUERTO RICO DURING THE NEXT SEVERAL HOURS. TROPICAL STORM
CONDITIONS ARE EXPECTED TO REACH THE DOMINICAN REPUBLIC LATER THIS
MORNING. TROPICAL STORM CONDITIONS ARE EXPECTED IN HAITI LATER
TODAY. TROPICAL STORM CONDITIONS ARE POSSIBLE IN THE SOUTHEASTERN
BAHAMAS...THE TURKS AND CAICOS...AND PORTIONS OF THE CENTRAL
BAHAMAS ON THURSDAY.
STORM SURGE...A STORM SURGE...ACCOMPANIED BY DANGEROUS WAVES...WILL
RAISE WATER LEVELS BY AS MUCH AS 1 TO 3 FEET IN THE TROPICAL STORM
RAINFALL...CHANTAL IS EXPECTED TO PRODUCE TOTAL RAIN ACCUMULATIONS
3 TO 6 INCHES OVER PUERTO RICO...THE U.S. VIRGIN ISLANDS...THE
SOUTHEASTERN BAHAMAS...THE DOMINICAN REPUBLIC AND HAITI. ISOLATED
MAXIMUM AMOUNTS OF 10 INCHES ARE POSSIBLE OVER HISPANIOLA.
NEXT COMPLETE ADVISORY...500 AM AST.
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