According to the latest storm track update from the National Hurricane Center, Tropical Storm Ana could become a category 2 hurricane.

TROPICAL STORM ANA DISCUSSION NUMBER 13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009
500 AM AST SAT AUG 15 2009

SATELLITE IMAGES INDICATE THAT THE TROPICAL DEPRESSION HAS CONTINUED TO BECOME BETTER ORGANIZED AND IS NOW UPGRADED TO TROPICAL STORM ANA. THE STORM IS DISPLAYING IMPROVED BANDING IN THE WESTERN SEMICIRCLE ALONG WITH A BALL OF CONVECTION NEAR THE CENTER.

NOAA BUOY 41041 REPORTED A MINIMUM PRESSURE OF ABOUT 1005 MB AS THE DEPRESSION PASSED VERY NEAR THE BUOY.

THE INITIAL INTENSITY IS RAISED TO 35 KT FOR THIS ADVISORY IN AGREEMENT WITH DVORAK INTENSITY ESTIMATES FROM SAB AND TAFB.

THE INITIAL MOTION ESTIMATE IS 270/14. THE GLOBAL MODELS ARE IN AGREEMENT THAT A DEEP-LAYER RIDGE WILL STRENGTHEN NORTH OF THE TROPICAL CYCLONE OVER THE NEXT DAY OR SO.

THIS PATTERN FAVORS THE TRACK OF ANA GRADUALLY BENDING FROM A WEST TO A WEST-NORTHWEST DIRECTION WITH AN INCREASE IN FORWARD SPEED.

THE ONLY SIGNIFICANT OUTLIERS TO THIS TRACK ARE THE GFDL AND GFS…WHICH BOTH WEAKEN THE SYSTEM RATHER QUICKLY…LEADING TO A MORE WESTWARD TRACK OF THE CYCLONE.

IN A FEW DAYS…SOME OF THE MODELS…SUCH AS THE GFS…SHOW A WEAKNESS IN THE RIDGE OVER THE WESTERN ATLANTIC THAT COULD ALLOW THE CYCLONE TO GAIN A LITTLE MORE LATITUDE.

THIS WEAKNESS APPEARS TO BE CAUSED BY THE MID- TO UPPER-LEVEL LOW CURRENTLY NEAR 25N 65W.

HOWEVER…THE MAJORITY OF THE GUIDANCE SHOWS THE MID- TO UPPER-LEVEL LOW MOVING WEST-SOUTHWESTWARD WITH MINIMAL INFLUENCE ON THE STRENGTH OF THE RIDGE.

GENERALLY…THE MODELS THAT HOLD ONTO ANA ARE IN GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD.

THE NHC TRACK FORECAST IS SHIFTED TOWARD THE SOUTHWEST FOR THIS ADVISORY…BUT NOT AS FAR AS THE MODEL CONSENSUS.

THE 0000 UTC GLOBAL MODELS GENERALLY FORECAST A MORE CONDUCIVE ENVIRONMENT FOR STRENGTHENING THAN PREVIOUS CYCLES…SHOWING A WEAKER MID-OCEANIC TROUGH AFFECTING THE SYSTEM.

IN PARTICULAR…THE UKMET AND NOGAPS BUILD UPPER-RIDGING NEAR THE CYCLONE WITH LIGHT SHEAR THROUGH THE PERIOD. HOWEVER…THE ECMWF SHOWS SOME WESTERLY SHEAR DEVELOPING IN ABOUT A DAY…BUT EVEN THAT MODEL HAS LIGHTER SHEAR CONDITIONS IN A FEW DAYS.

THE INTENSITY GUIDANCE RUNS THE FULL SPECTRUM THIS MORNING…WITH THE GFDL DISSIPATING THE SYSTEM…WHILE THE HWRF SHOWS A CATEGORY TWO HURRICANE BY THE END OF THE FORECAST PERIOD.

GIVEN THE UNCERTAINTY IN THE UPPER-LEVEL ENVIRONMENT LATER IN THE FORECAST PERIOD…THE OFFICIAL INTENSITY FORECAST IS INCREASED CONSERVATIVELY…IN BEST AGREEMENT WITH THE SHIPS MODEL BUT BELOW THE INTENSITY CONSENSUS.

A TROPICAL STORM WATCH MAY BE REQUIRED FOR PORTIONS OF THE LEEWARD ISLANDS LATER TODAY.

TS ANA FORECAST POSITIONS AND MAX WINDS

INITIAL 15/0900Z 14.6N 46.8W 35 KT
12HR VT 15/1800Z 14.7N 49.4W 40 KT
24HR VT 16/0600Z 15.3N 52.7W 45 KT
36HR VT 16/1800Z 16.1N 56.4W 45 KT
48HR VT 17/0600Z 17.0N 60.0W 50 KT
72HR VT 18/0600Z 19.5N 67.0W 55 KT
96HR VT 19/0600Z 22.5N 73.0W 60 KT
120HR VT 20/0600Z 26.0N 78.5W 60 KT