Caribbean-On-Line's Caribbean Hurricane Blog



Tropical Storm Dorian

Remnants of Dorian

Published on July 29, 2013 6:46 PM | Comments

The NHC is reporting on the remains of Dorian:

DATA FROM THE AIR FORCE RECONNAISSANCE AIRCRAFT INVESTIGATING THE REMNANTS OF DORIAN...LOCATED A COUPLE OF HUNDRED MILES NORTH OF PUERTO RICO...CONFIRM THAT THE SYSTEM DOES NOT HAVE A CLOSED LOW-LEVEL CIRCULATION. IN ADDITION...THE DISTURBANCE IS POORLY ORGANIZED WITH THE LOWEST SURFACE PRESSURES WELL REMOVED FROM THE MAIN AREA OF THUNDERSTORMS.

UPPER-LEVEL WINDS ARE NOT PARTICULARLY CONDUCIVE FOR REGENERATION TO
OCCUR. THIS SYSTEM HAS A MEDIUM CHANCE...30 PERCENT...OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS. THE REMNANTS OF DORIAN
ARE EXPECTED TO MOVE WEST-NORTHWESTWARD OVER THE NEXT COUPLE OF
DAYS. SHOWERS AND GUSTY WINDS TO NEAR GALE FORCE IN SQUALLS ARE
EXPECTED TO STAY WELL TO THE NORTH OF PUERTO RICO TODAY...AND COULD
SPREAD ACROSS THE TURKS AND CAICOS ISLANDS AND PORTIONS OF THE
BAHAMAS TONIGHT THROUGH WEDNESDAY. ADDITIONAL INFORMATION ON THIS
SYSTEM CAN BE FOUND IN HIGH SEAS FORECASTS ISSUED BY THE NATIONAL
WEATHER SERVICE.

To me I think it is sort of strange that they (the NHC) come out with these storm tracks as soon as a storm is formed, when so many of the storms disappear, and they were never on good footing to begin with (meaning, yes, a tropical depression turned into a storm, but the environmental conditions and models clearly showed that it would not last). The ECMWF (which has been spot on with hurricanes the last couple of years) had Dorian as a not event from the beginning, yet their forecast seemed to be pretty much ignored by the NHC.



TROPICAL STORM DORIAN DISCUSSION NUMBER 7

Published on July 25, 2013 10:40 PM | Comments

TROPICAL STORM DORIAN DISCUSSION NUMBER 7
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013
500 PM AST THU JUL 25 2013

AFTER A BRIEF DISRUPTION IN THE INNER CORE CONVECTIVE PATTERN
EARLIER THIS AFTERNOON...DORIAN HAS MADE A COMEBACK WITH A BURST OF
COLD-TOPPED CONVECTION DEVELOPING OVER THE PREVIOUSLY EXPOSED
LOW-LEVEL CENTER. IN ADDITION...A 1728Z TRMM OVERPASS INDICATED A
NEARLY CLOSED LOW-LEVEL EYE HAD DEVELOPED BENEATH A WEAK MID-LEVEL
EYE FEATURE. SATELLITE CURRENT INTENSITY ESTIMATES REMAIN AT 55 KT
AND 45 KT FROM TAFB AND SAB...RESPECTIVELY...AND AN EARLIER ASCAT-B
OVERPASS AT 1230Z INDICATED SURFACE WINDS OF AT LEAST 48 KT NORTH
OF THE CENTER. BASED ON THESE DATA...THE INITIAL INTENSITY REMAINS
50 KT FOR THIS ADVISORY.

THE INITIAL MOTION ESTIMATE IS 290/16. SEVERAL OF THE MORE RELIABLE
MODELS...SUCH AS THE GFS RUN OFF THE NEW WCOSS SUPERCOMPUTER...MADE
A SIGNIFICANT SOUTHWARD SHIFT ON THE 12Z MODEL CYCLE. HOWEVER...THE
OVERALL GUIDANCE ENVELOPE DID NOT SHIFT SOUTHWARD...BUT RATHER
CONVERGED EVEN MORE TIGHTLY AROUND THE PREVIOUS NHC FORECAST
TRACKS. AS A RESULT...ESSENTIALLY NO CHANGES WERE MADE TO THE
PREVIOUS FORECAST TRACK OR REASONING. AS MENTIONED IN PREVIOUS
DISCUSSIONS...THE MAIN DIFFERENCE BETWEEN THE MODELS CONTINUES TO
BE THE FORWARD SPEED OF DORIAN. THE ECMWF IS ONE OF THE FASTER
MODELS SINCE IT WEAKENS DORIAN ALMOST IMMEDIATELY AND MOVES IT
QUICKLY IN THE BRISK EASTERLY TRADE WIND FLOW...WHEREAS THE UKMET
AND HWRF MODELS MAINTAIN A VERTICALLY DEEPER AND MORE ROBUST
TROPICAL CYCLONE... WHICH MOVES SLOWER IN THE DEEP-LAYER STEERING
FLOW. GIVEN THAT THE GFS-ENSEMBLE MEAN...HWRF...AND UKMET MODELS
HAVE HANDLED THE INTENSITY AND TRACK OF DORIAN THE BEST THUS
FAR...THE OFFICIAL FORECAST LEANS CLOSER TO THOSE SOLUTIONS. THE
NEW ADVISORY TRACK IS JUST AN UPDATE OF THE PREVIOUS FORECAST...AND
IS IDENTICAL TO BUT REMAINS A LITTLE SLOWER THAN THE CONSENSUS
TRACK MODEL TVCN.

AFTER SURVIVING THE DIURNAL CONVECTIVE MINIMUM PERIOD...DORIAN IS
NOW MOVING OVER 26C SSTS AND TOWARD EVEN WARMER WATERS...AND ALSO
INTO THE CONVECTIVE MAXIMUM PERIOD. DORIAN IS FORECAST TO REMAIN IN
A LOW SHEAR ENVIRONMENT FOR ANOTHER 72-96 HOURS...DURING WHICH TIME
AT LEAST SOME GRADUAL STRENGTHENING IS EXPECTED AS THE CYCLONE
MOVES OVER SSTS ABOVE 27C. BY DAY 5...THE UPPER-LEVEL FLOW PATTERN
IS QUITE UNCERTAIN WITH DORIAN POSSIBLY MOVING INTO SOME MODERATE
TO STRONG SOUTHWESTERLY SHEAR CONDITIONS ACCORDING TO THE GFS AND
ECMWF MODELS. GIVEN THIS...THE OFFICIAL FORECAST ONLY SHOWS MODEST
STRENGTHENING AND MAINLY FOLLOWS THE LGEM...SHIPS...AND HWRF
MODELS.



Tropical Storm Dorian latest visible satellite image

Published on July 25, 2013 10:15 AM | Comments



Dorian forecast

Published on July 25, 2013 9:59 AM | Comments

Dorian is currently forecast to remain a tropical storm, and track above the Caribbean islands. The NHC (see below) does not have strong confidence in this forecast at this point. On the current track the Turks & Caicos and the Bahamas look to be in the potential path of this storm.

TROPICAL STORM DORIAN DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013 500 AM AST THU JUL 25 2013

DORIAN HAS BECOME A LITTLE BETTER ORGANIZED THIS MORNING...WITH STRONGER CONVECTION OCCURRING NEAR THE CENTER. A RECENT AMSU OVERPASS SHOWED A MID-LEVEL EYE ASSOCIATED WITH THIS CONVECTION... ALTHOUGH IT WAS UNCLEAR IF THIS FEATURE WAS DIRECTLY OVER THE LOW-LEVEL CENTER. SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM SAB AND 45 KT FROM TAFB...AND A RECENT AMSU-BASED INTENSITY ESTIMATE FROM CIMSS WAS 48 KT. BASED ON THIS THE INITIAL INTENSITY IS INCREASED TO 50 KT.

THE INITIAL MOTION IS 290/15. DORIAN IS ON THE SOUTH SIDE OF A DEEP-LAYER RIDGE THAT COVERS THE CENTRAL AND EASTERN ATLANTIC. THIS FEATURE SHOULD STEER THE CYCLONE QUICKLY WEST-NORTHWESTWARD TO WESTWARD FOR THE NEXT 72 HOURS OR SO. AFTER THAT...DORIAN SHOULD APPROACH A WEAKNESS IN THE RIDGE...WHICH SHOULD LEAD TO A WEST-NORTHWESTWARD MOTION AT A DECREASED FORWARD SPEED. THE GUIDANCE ENVELOPE HAS SHIFTED A BIT TO THE NORTH SINCE THE PREVIOUS ADVISORY. BASED ON THIS...THE NEW FORECAST TRACK WILL BE NUDGED A LITTLE TO THE NORTH...BUT IT LIES SOUTH OF THE CENTER OF THE GUIDANCE ENVELOPE AND THE MODEL CONSENSUS.

THE INTENSITY FORECAST IS COMPLEX AND OF LOW CONFIDENCE. DORIAN SHOULD MOVE OVER WARMER SEA SURFACE TEMPERATURES DURING THE NEXT 2-3 DAYS...BUT DURING THIS TIME IT ALSO MAY ENCOUNTER SOUTHWESTERLY VERTICAL WIND SHEAR AND DRIER AIR AT THE MID-LEVELS. IN ADDITION...THE UPPER-LEVEL WIND FORECASTS FROM THE DYNAMICAL MODELS BECOME QUITE DIVERGENT BETWEEN 72-120 HOURS...WITH THE POSSIBILITIES RANGING FROM CONDITIONS FAVORABLE FOR INTENSIFICATION TO SHEAR STRONG ENOUGH TO CAUSE DORIAN TO WEAKEN. OVERALL...THE INTENSITY GUIDANCE FORECASTS LITTLE CHANGE IN STRENGTH DURING THE NEXT FIVE DAYS...AND THUS THE NEW FORECAST IS THE SAME AS THE PREVIOUS FORECAST. THE NEW FORECAST IS IN BEST AGREEMENT WITH THE SHIPS MODEL AND IS STRONGER THAN THE INTENSITY CONSENSUS.



Tropical Storm Dorian forms in the Atlantic

Published on July 24, 2013 11:26 AM | Comments

It is official - Tropical Storm Dorian has formed in the Atlantic. At this point the forecast seems to be calling for a tropical storm and not a hurricane, tracking just north of the Virgin Islands. We'll be keeping an eye on it:

TROPICAL DEPRESSION FOUR DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013
500 AM EDT WED JUL 24 2013

GEOSTATIONARY SATELLITE IMAGES SHOW THAT THE DEEP CONVECTION
ASSOCIATED WITH THE LOW PRESSURE SYSTEM OVER THE EASTERN ATLANTIC
HAS INCREASED IN COVERAGE AND BECOME MORE CONCENTRATED NEAR THE
CENTER OVERNIGHT AND EARLY THIS MORNING. EARLIER SCATTEROMETER
DATA INDICATED THAT THE SYSTEM HAD A WELL-DEFINED CENTER AND
MAXIMUM WINDS OF AROUND 30 KT. BASED ON THESE DATA...THE SYSTEM IS
NOW BEING CLASSIFIED AS A TROPICAL DEPRESSION.

THE DEPRESSION IS MOVING WEST-NORTHWESTWARD OR 285 DEGREES AT
17 KT. THE CYCLONE IS EXPECTED TO BE STEERED WESTWARD OR WEST-
NORTHWESTWARD TO THE SOUTH OF A LARGE DEEP-LAYER RIDGE OVER
THE CENTRAL AND EASTERN ATLANTIC. THE DYNAMICAL MODEL GUIDANCE
IS IN VERY GOOD AGREEMENT ON THIS SCENARIO...ALTHOUGH THERE ARE
SOME DIFFERENCES IN HOW FAST THE CYCLONE MOVES WESTWARD. THE GFS
AND ECMWF SHOW A FASTER FORWARD MOTION THAN MOST OF THE OTHER
TRACK MODELS. AS A RESULT...THE NHC FORECAST LEANS TOWARD THESE
TYPICALLY RELIABLE MODELS AND SHOWS A FASTER WESTWARD MOTION THAN
THE MULTI-MODEL CONSENSUS.

THE INTENSITY FORECAST IS OF LOWER CONFIDENCE THAN THE TRACK
FORECAST. ALTHOUGH THE SHEAR IS EXPECTED TO REMAIN LOW DURING THE
NEXT FEW DAYS...THE CYCLONE WILL BE MOVING OVER SLIGHTLY COOLER
WATERS AND INTO A LITTLE DRIER ENVIRONMENT OVER THE NEXT
DAY OR TWO. THEREFORE...ONLY SLIGHT STRENGTHENING IS INDICATED
IN THE NHC FORECAST. LATER IN THE FORECAST PERIOD...THE CYCLONE
IS EXPECTED TO APPROACH AN UPPER-LEVEL TROUGH OVER THE WEST-CENTRAL
ATLANTIC WHICH COULD CAUSE AN INCREASE IN SOUTHWESTERLY SHEAR.
BECAUSE OF THIS...THE NHC FORECAST SHOWS LITTLE CHANGE IN STRENGTH
DURING THE 3 TO 5 DAY TIME PERIOD.

FORECAST POSITIONS AND MAX WINDS

INIT 24/0900Z 13.9N 28.1W 30 KT 35 MPH
12H 24/1800Z 14.6N 30.8W 35 KT 40 MPH
24H 25/0600Z 15.5N 34.4W 40 KT 45 MPH
36H 25/1800Z 16.2N 37.8W 40 KT 45 MPH
48H 26/0600Z 16.8N 41.2W 40 KT 45 MPH
72H 27/0600Z 18.2N 49.0W 40 KT 45 MPH
96H 28/0600Z 19.3N 56.5W 40 KT 45 MPH
120H 29/0600Z 20.0N 62.0W 40 KT 45 MPH