Tropical Storm Dorian Forms… Wednesday Morning Update – 11am

The National Hurricane Center has upgraded Tropical Depression # 4 into Tropical Storm Dorian this morning. The storm is gradually becoming better organized, but the environment isn’t favorable for this system to become a strong hurricane over the next few days. There’s some dry air near the center, wind shear will be increasing and water temperatures are rather cool in that part of the Atlantic. Dorian has winds of 50 mph, as it tracks west northwest at 21mph. There’s a good chance this system will weaken as it encounters stronger shear in a few days… We’ll keep a close eye on it, but Dorian is way out there. We’ve got lots of time before it gets anywhere near the US, if it even survives at all. Here’s a discussion from the National Hurricane Center:

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

Richard Scott

WVUA Chief Meteorologist