[Tropical] Tropical Cyclone Discussion

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WTNT45 KNHC 072102
TCDAT5

TROPICAL STORM NATE DISCUSSION NUMBER   1
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL152011
400 PM CDT WED SEP 07 2011

SATELLITE IMAGES INDICATE THAT THE AREA OF LOW PRESSURE IN THE BAY
OF CAMPECHE HAS BECOME BETTER ORGANIZED WITH CURVED BANDING
FEATURES NOTED.  SURFACE OBSERVATIONS FROM LAND AND PEMEX OIL
RIGS...ALONG WITH AIR FORCE RESERVE RECONNAISSANCE AIRCRAFT
DATA...SHOW THAT THE LOW-LEVEL CIRCULATION IS WELL DEFINED...WITH
LITTLE TEMPERATURE GRADIENT NOTED.  THUS ADVISORIES ARE INITIATED
ON THIS SYSTEM.  SINCE THE RECON PLANE FOUND 53 KT AT FLIGHT LEVEL
ALONG WITH SFMR VALUES OF 40 TO 45 KT...THE CYCLONE IS BEING NAMED
NATE WITH A CONSERVATIVE INITIAL WIND SPEED OF 40 KT.

NATE IS FORECAST TO BE OVER VERY WARM WATERS WITH LITTLE VERTICAL
WIND SHEAR FOR THE NEXT FEW DAYS.  THE ONLY SIGNIFICANT INHIBITING
FACTOR IS A LARGE AREA OF DRY AIR SEEN IN WATER VAPOR IMAGES
NORTHWEST OF THE SYSTEM.  HOWEVER...THIS DRY AIR WILL TAKE SOME
TIME TO WORK ITS WAY INTO THE CENTER...IF AT ALL...IN A LOW SHEAR
ENVIRONMENT.  MOST MODELS SHOW INTENSIFICATION THROUGHOUT THE
FORECAST PERIOD...AND THE OFFICIAL FORECAST IS CLOSE TO A BLEND OF
THE LGEM AND SHIPS MODELS.

THE CYCLONE HAS BEEN DRIFTING DURING THE DAY...WITH A LONG-TERM
MOTION OF ABOUT 110/2.  NATE IS IN AN AREA OF VERY WEAK STEERING
FLOW BETWEEN THE REMNANTS OF LEE OVER THE EASTERN UNITED STATES AND
A RIDGE OVER NORTHERN MEXICO.  LITTLE NET MOTION IS EXPECTED FOR
THE NEXT DAY OR SO DUE TO THIS PATTERN.  AFTER THAT TIME...A RIDGE
OVER THE WESTERN CARIBBEAN IS FORECAST TO BUILD...WHICH SHOULD
CAUSE NATE TO MOVE MORE TOWARD THE NORTH...EVENTUALLY BENDING TO
THE LEFT AS THE CYCLONE COMES UNDER THE INFLUENCE OF THE MEXICAN
RIDGE.  THERE IS A FAIR AMOUNT OF SPREAD IN THE GUIDANCE DUE TO THE
STRENGTH OF THE RIDGES...AND THE OFFICIAL FORECAST IS CLOSEST TO
THE HFIP MODEL CONSENSUS...A BIT SOUTH OF THE ECMWF MODEL.


FORECAST POSITIONS AND MAX WINDS

INIT  07/2100Z 20.2N  92.4W   40 KT  45 MPH
 12H  08/0600Z 20.0N  92.1W   45 KT  50 MPH
 24H  08/1800Z 20.1N  91.9W   50 KT  60 MPH
 36H  09/0600Z 20.4N  92.1W   60 KT  70 MPH
 48H  09/1800Z 21.0N  92.5W   65 KT  75 MPH
 72H  10/1800Z 22.5N  93.5W   70 KT  80 MPH
 96H  11/1800Z 23.0N  95.0W   75 KT  85 MPH
120H  12/1800Z 23.0N  96.5W   75 KT  85 MPH

$$
FORECASTER BLAKE/ZELINSKY


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