Former TS Dorian

[srainhoutx]

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AL, 98, 2013072118, , BEST, 0, 127N, 141W, 20, 1012, DB, 0, , 0, 0, 0, 0,
AL, 98, 2013072200, , BEST, 0, 127N, 151W, 20, 1011, DB, 0, , 0, 0, 0, 0,
AL, 98, 2013072206, , BEST, 0, 127N, 161W, 20, 1011, DB, 0, , 0, 0, 0, 0,
AL, 98, 2013072212, , BEST, 0, 127N, 171W, 20, 1010, DB,

[srainhoutx]

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT MON JUL 22 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

1. A TROPICAL WAVE ACCOMPANIED BY A SURFACE LOW PRESSURE SYSTEM IS
LOCATED ABOUT 400 MILES EAST-SOUTHEAST OF THE CAPE VERDE ISLANDS.
THUNDERSTORM ACTIVITY HAS INCREASED AND BECOME BETTER ORGANIZED
TODAY...AND ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE FAVORABLE
FOR DEVELOPMENT OVER THE NEXT DAY OR SO BEFORE BECOMING LESS
CONDUCIVE LATER IN THE WEEK. THIS SYSTEM HAS A MEDIUM CHANCE...
30 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS
AS IT MOVES WESTWARD AT ABOUT 15 MPH. INTERESTS IN THE CAPE VERDE
ISLANDS SHOULD MONITOR THE PROGRESS OF THIS DISTURBANCE.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

FORECASTER STEWART

[srainhoutx]

[srainhoutx]

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT TUE JUL 23 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A SURFACE LOW PRESSURE SYSTEM LOCATED A COUPLE OF HUNDRED MILES
SOUTH OF THE CAPE VERDE ISLANDS IS MOVING WESTWARD AT ABOUT 10 MPH.
THIS SYSTEM HAS A WELL-DEFINED CIRCULATION...AND ONLY A SMALL
INCREASE IN THE AMOUNT AND ORGANIZATION OF THE THUNDERSTORM
ACTIVITY WOULD RESULT IN THE FORMATION OF A TROPICAL DEPRESSION.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE FAVORABLE FOR
DEVELOPMENT DURING THE NEXT DAY OR SO BEFORE UPPER-LEVEL WINDS AND
OCEAN TEMPERATURES BECOME LESS CONDUCIVE BY THURSDAY. THIS SYSTEM
HAS A HIGH CHANCE...60 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER STEWART

[Katdaddy]

Back to a normal Summertime pattern across TX. Watching the tropics this evening as Invest 98L is approaching TD status. Will 98L reach TD status before SAL (Saharan Air Layer - very dry, warm, dusty air that tropical cyclones hate) wins? Models show a W bend into the NE Caribbean of whatever is left. Its getting to that time of year again. Something to watch for now.

[srainhoutx]

Convection is beginning to fire near the center of circulation and ASCAT pass confirms a closed low. I believe we will see a Ttropical Depression within the next 12-24 hours. Should the more southern track verify, the Caribbean Islands may see a Tropical Storm approaching this weekend. The one limiting factor is a TUTT low traveling in tandem to the W ahead of 98L. I believe the SAL issue is not that big of an issue as long as it remains along 12N. A recurving storm is becoming a bit less likely as well, IMO.

[srainhoutx]

 

000
WTNT44 KNHC 240841
TCDAT4

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

$$
FORECASTER BROWN

[Katdaddy]

TD 4 is official at 5AM. Models bring TD 4 to TS status over the next few days and continue a more W motion later in the forecast period. It would at least a week from tomorrow before it would enter the GOM at this point. Plenty of time to watch.

[srainhoutx]

[srainhoutx]

Conditions appear to be improving for TD 4 and perhaps we'll see Tropical Storm Dorian before the day is done.

[srainhoutx]

12Z Tropical Guidance has updated and now has Tropical Storm Dorian. Waiting on the official update from the NHC.

[wxman57]

Latest model guidance initialized at 45 kts (50 mph). Looks like a good estimate to me. It's a small storm. Distance across the core is only 75 miles. Total width including that long spiral band to the south is 150 miles.

[srainhoutx]

TROPICAL STORM DORIAN DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013
1100 AM EDT WED JUL 24 2013

VISIBLE SATELLITE IMAGERY AND RECENT ASCAT SCATTEROMETER WINDS
INDICATE THAT THE TROPICAL DEPRESSION HAS BECOME BETTER ORGANIZED
AND HAS STRENGTHENED INTO TROPICAL STORM DORIAN. THE INITIAL
INTENSITY OF 45 KT IS BASED ON A 38-KT ASCAT SURFACE WIND AT
1111Z... AND VARIOUS OBJECTIVE SATELLITE INTENSITY ESTIMATES OF
ABOUT 45 KT.

THE INITIAL MOTION ESTIMATE IS 285/18 KT. DORIAN IS EXPECTED TO BE
STEERED WEST-NORTHWESTWARD TO WESTWARD BY A STRONG DEEP-LAYER
SUBTROPICAL RIDGE OVER THE CENTRAL AND EASTERN ATLANTIC. THE NHC
MODEL GUIDANCE REMAINS TIGHTLY PACKED IN EXCELLENT AGREEMENT ON
THIS TRACK SCENARIO...WITH THE ONLY DIFFERENCES BEING SLIGHT
VARIATIONS IN THE FORWARD SPEED. THE NHC OFFICIAL FORECAST TRACK IS
SIMILAR TO THE PREVIOUS ADVISORY AND IS CLOSE TO THE MULTI-MODEL
CONSENSUS TVCN.

FOR THE NEXT 24 HOURS OR SO...THE VERTICAL SHEAR IS FORECAST TO BE
VERY LOW WHILE DORIAN REMAINS OVER MARGINALLY WARM SSTS. HOWEVER...
DURING THE 24-48 HOUR TIME PERIOD...DORIAN WILL BE MOVING OVER 25C
SSTS...WHICH COULD INDUCE SOME SLIGHT WEAKENING. THE CYCLONE IS
EXPECTED TO MAINTAIN THE CURRENT FAVORABLE EQUATORIAL INFLOW OF
WARM UNSTABLE AIR THAT IS OFFSETTING THE COOLER MORE STABLE AIR
BEING INGESTED FROM THE NORTH...AND THAT COULD OFFSET THE EFFECTS
OF DORIAN PASSING OVER COOLER WATERS. FOR THAT REASON...THE
INTENSITY FORECAST ONLY SHOWS SLIGHT WEAKENING AT 36- AND 48-HOURS.
AFTER THAT...THE CYCLONE IS LIKELY TO ENCOUNTER BOTH WARMER WATER
AND INCREASING WESTERLY SHEAR...SO THE INTENSITY FORECAST IS HELD
STEADY. THE OFFICIAL INTENSITY FORECAST IS SLIGHTLY HIGHER THAN THE
PREVIOUS ADVISORY THROUGH THE NEXT 24 HOURS DUE TO THE HIGHER
INITIAL INTENSITY...BUT THEN FOLLOWS THE TREND OF CONSENSUS MODELS.

FORECAST POSITIONS AND MAX WINDS

INIT 24/1500Z 14.3N 29.9W 45 KT 50 MPH
12H 25/0000Z 15.0N 32.6W 50 KT 60 MPH
24H 25/1200Z 15.8N 36.1W 50 KT 60 MPH
36H 26/0000Z 16.4N 39.8W 45 KT 50 MPH
48H 26/1200Z 17.1N 43.4W 40 KT 45 MPH
72H 27/1200Z 18.3N 51.2W 40 KT 45 MPH
96H 28/1200Z 19.3N 58.2W 40 KT 45 MPH
120H 29/1200Z 20.1N 64.0W 40 KT 45 MPH

$$
FORECASTER STEWART

[srainhoutx]

TROPICAL STORM DORIAN DISCUSSION NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042013
500 PM EDT WED JUL 24 2013

CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY INDICATE THAT THE
CONVECTIVE STRUCTURE OF DORIAN HAS CHANGED LITTLE SINCE THE
PREVIOUS ADVISORY. HOWEVER...UPPER-LEVEL ANTICYCLONIC OUTFLOW HAS
IMPROVED IN ALL QUADRANTS AS THE VERTICAL SHEAR HAS DIMINISHED
SIGNIFICANTLY. THE INITIAL INTENSITY OF 45 KT IS BASED ON A
SATELLITE INTENSITY ESTIMATE OF T3.0/45 KT FROM TAFB.

THE INITIAL MOTION ESTIMATE IS 285/17 KT. DORIAN IS EXPECTED TO
REMAIN SOUTH OF AND MOVE WEST-NORTHWESTWARD TO WESTWARD IN TANDEM
WITH A STRONG SUBTROPICAL RIDGE LOCATED WELL TO THE NORTH. THE NHC
MODEL GUIDANCE CONTINUES TO REMAIN TIGHTLY PACKED AND IN EXCELLENT
AGREEMENT ON THIS SCENARIO. THE ONLY DIFFERENCES IN THE MODELS ARE
THE FORWARD SPEED...WHICH IS DUE TO THE STRENGTH AND VERTICAL DEPTH
OF DORIAN. THE GFS...UKMET...AND CANADIAN MODELS MAINTAIN A ROBUST
AND MORE VERTICALLY DEEP CYCLONE...WHICH GETS STEERED MORE SLOWLY
BY THE DEEPER MEAN FLOW. IN CONTRAST...THE HWRF AND ECMWF MODELS
WEAKEN DORIAN SIGNIFICANTLY AS THE CYCLONE PASSES OVER COOLER WATER
DURING THE NEXT 48 HOURS...WHICH RESULTS IN A SHALLOWER AND WEAKER
VORTEX BEING STEERED MORE RAPIDLY WESTWARD BY THE STRONGER EASTERLY
TRADE WIND FLOW. GIVEN THAT DORIAN WILL BE MOVING OVER COOLER WATER
AT A BRISK 18 KT FOR THE NEXT 24-36 HOURS...MY FEELING IS THAT THE
CYCLONE WILL NOT WEAKEN AS MUCH AS THE SOME OF THE MODELS ARE
FORECASTING...AND AS A RESULT...THE OFFICIAL TRACK FORECAST LEANS
TOWARD THE SLOWER GFS...UKMET...AND CANADIAN MODEL SOLUTIONS.

DORIAN IS BEGINNING TO MOVE OVER SUB-26C SSTS...AND THE CYCLONE
SHOULD REMAIN OVER COOLER WATERS NEAR 25C FOR THE NEXT 12 HOURS
OR SO...WHICH COULD INDUCE SOME SLIGHT WEAKENING. HOWEVER...BY 36-48
HOURS...DORIAN WILL BE MOVING BACK OVER SSTS WARMER THAN 26C AND IN
A VERY LOW VERTICAL SHEAR ENVIRONMENT...WHICH SHOULD ALLOW FOR SOME
RE-STRENGTHENING TO OCCUR. THE LATEST RUNS OF THE GFS AND ECMWF
ARE SHOWING A LESS HOSTILE UPPER-AIR PATTERN NEAR THE END OF THE
FORECAST PERIOD...WITH MORE RIDGING AND LESS INFLUENCE FROM AN
UPPER-LEVEL TROUGH OVER THE BAHAMAS. IN CONSIDERATION OF THAT...
THE FORECAST INTENSITIES AT DAYS 4-5 HAVE BEEN INCREASED RELATIVE
TO THE PREVIOUS ADVISORY.

FORECAST POSITIONS AND MAX WINDS

INIT 24/2100Z 14.6N 31.4W 45 KT 50 MPH
12H 25/0600Z 15.3N 34.0W 45 KT 50 MPH
24H 25/1800Z 16.1N 37.5W 40 KT 45 MPH
36H 26/0600Z 16.8N 41.0W 40 KT 45 MPH
48H 26/1800Z 17.5N 44.7W 45 KT 50 MPH
72H 27/1800Z 18.7N 51.8W 45 KT 50 MPH
96H 28/1800Z 19.6N 58.9W 50 KT 60 MPH
120H 29/1800Z 20.0N 64.0W 50 KT 60 MPH

$$
FORECASTER STEWART

[srainhoutx]

Sunset across the Atlantic on Dorian. I've also noticed a bit of a spin around 10N and 35W or SW of TS Dorian. This feature exited Africa a day or two before the main circulation that became Dorian and is near the ITCZ.

[srainhoutx]

Afternoon e-mail update from Jeff:

4th tropical storm of the Atlantic hurricane season forms over the far eastern Atlantic Ocean about 500 miles W of the Cape Verde Islands.

Discussion:
TD # 4 was upgraded to a tropical storm this morning at 1000am. Since then the system has maintained or increased its upper level outflow in all sections of the system and has exhibited a ball of deep convection near/over the center. Dorian is moving W to WNW at a fast rate of speed (20mph) and this motion should continue.

Track:
Dorian is located south of a powerful north Atlantic ridge of high pressure and this high pressure cell is forecast to move generally W in conjunction with the W to WNW movement of Dorian. Global model track guidance is very well clustered through the next 3 days on the system crossing the open Atlantic Ocean. The models begin to diverge toward the end of the 5-day forecast period in which their handling of troughing currently along the US east coast comes into question. For not the forecast track through day 5 is of fairly high confidence and supported by good model agreement.

Intensity:
Dorian is a small compact small currently which can respond quickly to environmental changes around the circulation (dry air or wind shear) and this response can be both on the sides of rapid weakening or rapid intensification. Ahead of the system is a large mass of dry air that moved off the African coast a few days ago and this dry air may at times become ingested into the circulation. However small systems tend to be able to “protect” themselves at times from such dry air intrusions and thus far Dorian is holding its own. Dorian will also be crossing water temperatures currently marginal for development, but I think this will have a lower impact compared to the dry air. Wind shear is light currently with favorable outflow so if a well-defined inner core can develop, Dorian will begin to intensify especially once west of the cooler waters. Nearly all of the intensity guidance keep Dorian as a tropical storm for the next 5 days and in fact the ECMWF model (a highly respected model) weakens the system into an open wave. Given the support by the other guidance and the robust circulation associated with the system I am leaning away from the ECMWF suggesting of an open wave in favor of a closed system. With that said if dry air does wrap into the inner core then there could be some issues for the system over the next 3-4 days.

NOTE: now is a good time to remind all that the error cone represented in the NHC forecast track below is just that (the average of the track error by time over the last 5 years). It in no way represents the potential impacts (rainfall, wind, storm surge) from a tropical cyclone.

NHC Forecast Track and Error Cone:

[Paul Robison]

Hmmm.....

[srainhoutx]

The 12Z Track and Intensity guidance suggest a general WNW motion and little in the way of strengthening as it nears the Turks & Caicos in the SE Bahamas.

[wxman57]

Assuming Dorian survives for a week, the most likely scenario remains a recurve near the Bahamas and no Gulf entry.

[wxman57]

Some climo fun from Coastal Services Center. I plotted all storms which passed within 150NM (about 180 miles) from Dorian's current point. 93 such storms were found. Of those, only 2 entered the Gulf - Ike (2008) and the 1915 Galveston hurricane. From this, we can conclude that:

There is about a 2.15% chance that Dorian will enter the Gulf. However, if it does enter the Gulf, there is a 100% chance it will hit Houston/Galveston!