505
WTNT44 KNHC 110836
TCDAT4
TROPICAL STORM SEAN DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL192023
500 AM AST WED OCT 11 2023
SATELLITE IMAGES INDICATE THAT DEEP CONVECTION HAS INCREASED NEAR
THE CENTER OF THE CYCLONE, WITH SOME CURVED BANDING FEATURES
LOCATED BOTH NORTH AND SOUTH OF THE CENTER. SUBJECTIVE AND
OBJECTIVE DVORAK ESTIMATES FROM TAFB/SAB/UW-CIMSS RANGE FROM 30-47
KT, AND A CONSERVATIVE BLEND OF THIS DATA GIVES AN INITIAL WIND
SPEED OF 35 KT FOR THIS ADVISORY. THUS TROPICAL STORM SEAN HAS
FORMED, THE 19TH NAMED STORM IN THIS BUSY 2023 ATLANTIC SEASON.
SEAN COULD INTENSIFY A BIT MORE DURING THE NEXT DAY OR SO BEFORE
INCREASING SOUTHERLY SHEAR AFFECTS THE CORE OF THE CYCLONE. SOME
HINTS OF THIS SHEAR CAN ALREADY BE SEEN IN CIRRUS CLOUD MOTIONS FROM
CONVECTIVE ACTIVITY NORTHWEST OF THE TROPICAL CYCLONE. THEREAFTER,
MODERATE-TO-STRONG SHEAR IS EXPECTED TO GENERALLY CANCEL OUT THE
ENHANCING EFFECTS OF A RELATIVELY MOIST AND UNSTABLE ENVIRONMENT,
LEADING TO LITTLE NET CHANGE FOR A FEW DAYS. BY THE END OF THE
WEEK, WHILE THE SHEAR COULD WEAKEN, GLOBAL MODELS ARE GENERALLY
SHOWING AN INFLUX OF DRIER MID-LEVEL AIR ALONG WITH UPPER-LEVEL
CONVERGENCE, WHICH WOULD TYPICALLY WEAKEN ANY ASSOCIATED DEEP
CONVECTION. MANY OF THE REGIONAL HURRICANE MODELS, HOWEVER,
ACTUALLY SHOW SOME STRENGTHENING AT LONG RANGE, BUT THEY HAVE BEEN
INCONSISTENT AT THAT TIME FRAME. THE NHC FORECAST LEANS MORE ON
THE GLOBAL MODELS FOR NOW, SIMILAR TO THE PREVIOUS FORECAST AND THE
MODEL CONSENSUS, AND CONTINUES TO SHOW SEAN BECOMING A REMNANT LOW
ON DAY 5.
THE STORM IS MOVING WEST-NORTHWESTWARD AT ABOUT 11 KT. A MID-LEVEL
RIDGE LOCATED TO THE NORTHEAST OF THE CYCLONE SHOULD STEER SEAN
WEST-NORTHWESTWARD TO NORTHWESTWARD THROUGH FRIDAY. VERY LATE IN THE
FORECAST PERIOD, A BEND BACK TOWARD THE WEST-NORTHWEST IS
ANTICIPATED AS THE CYCLONE WEAKENS AND IS STEERED BY THE LOW-LEVEL
TRADE WIND FLOW. THE NEW NHC TRACK FORECAST IS ADJUSTED A BIT WEST
OF THE LAST ONE AT LONGER RANGE, BETWEEN THE MODEL-CONSENSUS AND
CORRECTED-CONSENSUS AIDS, WHICH FAVORS THE WEAKER TRACK AIDS ON THE
LEFT SIDE OF THE GUIDANCE ENVELOPE.
FORECAST POSITIONS AND MAX WINDS
INIT 11/0900Z 10.3N 33.1W 35 KT 40 MPH
12H 11/1800Z 10.7N 34.8W 40 KT 45 MPH
24H 12/0600Z 11.2N 36.5W 40 KT 45 MPH
36H 12/1800Z 11.8N 38.0W 40 KT 45 MPH
48H 13/0600Z 12.6N 39.5W 40 KT 45 MPH
60H 13/1800Z 13.5N 40.8W 40 KT 45 MPH
72H 14/0600Z 14.5N 42.0W 35 KT 40 MPH
96H 15/0600Z 16.7N 44.6W 35 KT 40 MPH
120H 16/0600Z 18.0N 47.0W 30 KT 35 MPH...POST-TROP/REMNT LOW
FORECASTER BLAKE
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