Tropical Storm ALVIN

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TROPICAL STORM ALVIN DISCUSSION NUMBER   4
NWS NATIONAL HURRICANE CENTER MIAMI FL       EP012013
200 AM PDT THU MAY 16 2013
 
ALVIN CONTINUES TO SLOWLY STRENGTHEN WITH SATELLITE IMAGES SHOWING
VERY DEEP CONVECTION RESEMBLING A CENTRAL DENSE OVERCAST.  MICROWAVE
PASSES...HOWEVER...SHOW A LESS ORGANIZED SYSTEM THAN A QUICK GLANCE
WOULD SUGGEST...WITH THE LOW-LEVEL CENTER DISPLACED A FAIR DISTANCE
WEST OF THE STRONGEST BURST.  ASCAT AND SATELLITE ESTIMATES SUGGEST
AN INTENSITY OF ABOUT 45 KT...SO THAT WILL BE THE INITIAL WIND
SPEED. 

CURRENT WATER VAPOR IMAGES SHOW A LOT OF UPPER-LEVEL WESTERLY WINDS
HEADED TOWARD THE CYCLONE...WITH SOME EVIDENCE OF THE FLOW ALREADY
IMPINGING ON THE CENTER.   THE FUTURE STRENGTH OF THE CYCLONE IS
NOT AN EASY FORECAST THIS MORNING WITH CONSIDERABLY MORE SHEAR IN
MOST OF THE MODEL FIELDS THAN YESTERDAY.  ALTHOUGH ALL OF THE
GUIDANCE CONTINUE TO SHOW SOME INTENSIFICATION...ONLY THE GFDL
MODEL REALLY SHOWS ALVIN BECOMING ANY MORE THAN A LOW-END CATEGORY
ONE HURRICANE.  THE NEW NHC FORECAST IS ABOUT THE SAME AS THE
PREVIOUS ONE FOR THE FIRST 24H...THEN IS REDUCED FOR THE REST OF
THE FORECAST PERIOD TO ACCOUNT FOR THE LATEST MODEL CONSENSUS
GUIDANCE.  WEAKENING SHOULD COMMENCE IN ABOUT 3 DAYS DUE TO
INCREASING WESTERLY SHEAR AND GRADUALLY DECREASING SSTS.

A BEVY OF ASCAT AND OTHER MICROWAVE DATA SHOW THAT ALVIN IS
MOVING A BIT SLOWER...290/9.  THIS GENERAL MOTION SEEMS PROBABLE
DURING THE NEXT COUPLE OF DAYS WHILE THE CYCLONE REMAINS SOUTH OF A
MID-LEVEL RIDGE OVER MEXICO.  AFTER THAT TIME...GLOBAL MODELS ARE
GENERALLY SHOWING LESS OF AN INTERACTION BETWEEN A TROUGH OVER THE
SOUTHWESTERN UNITED STATES AND ALVIN...WHICH RESULTS IN LESS OF A 
TURN TO THE NORTHWEST IN THE LONGER RANGE.  THE OFFICIAL FORECAST
HAS BEEN SHIFTED TO THE LEFT OF THE PREVIOUS ONE...FOLLOWING THE
TREND OF THE GUIDANCE...BUT IS GENERALLY TO THE RIGHT OF THE MODEL
CONSENSUS AFTER 24H.  
 
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  16/0900Z  9.1N 106.9W   45 KT  50 MPH
 12H  16/1800Z  9.5N 108.2W   50 KT  60 MPH
 24H  17/0600Z 10.2N 109.8W   60 KT  70 MPH
 36H  17/1800Z 11.0N 111.5W   65 KT  75 MPH
 48H  18/0600Z 11.6N 112.8W   65 KT  75 MPH
 72H  19/0600Z 12.8N 115.2W   60 KT  70 MPH
 96H  20/0600Z 14.0N 117.0W   40 KT  45 MPH
120H  21/0600Z 14.5N 118.5W   25 KT  30 MPH
 
$$
FORECASTER BLAKE
 
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