451
WTPZ43 KNHC 011448
TCDEP3
HURRICANE RACHEL DISCUSSION NUMBER 18
NWS NATIONAL HURRICANE CENTER MIAMI FL EP182026
800 AM MST THU OCT 01 2026
SATELLITE IMAGES SHOW THAT RACHEL CONTINUES TO PRODUCE DEEP
CONVECTION WITH COLD CLOUD TOPS NEAR -80 TO -85C. GLM LIGHTNING DATA
ALSO DEPICTS INCREASED LIGHTNING ACTIVITY IN THE INNER CORE OF THE
STORM. AN AMSR3 MICROWAVE PASS THAT ARRIVED SHORTLY AFTER THE
PREVIOUS ADVISORY INDICATED THAT THE LOW-LEVEL CENTER WAS SLIGHTLY
FARTHER EAST WITHIN THE DEEP CONVECTION AND, WHILE THERE STILL WAS
SOME TILT BETWEEN THE LOW- AND MID-LEVEL CORE, THE INNER STRUCTURE
IS BECOMING BETTER DEFINED, PARTICULARLY ON THE SOUTHERN SIDE OF THE
CIRCULATION. SATELLITE INTENSITY ESTIMATES HAVE INCREASED SLIGHTLY
AND VARY DEPENDING ON WHERE THE LOW-LEVEL CENTER IS PLACED. THE
SUBJECTIVE DVORAK SATELLITE INTENSITY ESTIMATE WAS DATA-T 5.0/90 KT
WITH A FINAL-T OF 4.5/77 KT, AND THE LAST THREE DMINT ESTIMATES
USING VARIOUS MICROWAVE IMAGES OVER THE PAST SEVERAL HOURS RANGED
BETWEEN 88-91 KT. GIVEN THE IMPROVED STRUCTURE IN THE MICROWAVE DATA
AND CURRENT SATELLITE TRENDS, THE INITIAL INTENSITY IS RAISED TO 90
KT FOR THIS ADVISORY.
THE SYSTEM CONTINUES TO MOVE WEST-NORTHWESTWARD, OR 295/5 KT, AND
THIS MOTION IS EXPECTED TO CONTINUE AT A SLIGHTLY SLOWER FORWARD
SPEED OVER THE NEXT COUPLE OF DAYS. AS A TROUGH OVER THE WESTERN
U.S. LIFTS NORTHEASTWARD, A MID-LEVEL RIDGE WILL BUILD TO THE NORTH
OF RACHEL, AND A WESTWARD MOTION AT AN INCREASED FORWARD SPEED IS
EXPECTED THROUGH THE END OF THE FORECAST PERIOD. THERE ARE SOME
ALONG-TRACK DIFFERENCES IN THE GUIDANCE THIS CYCLE REGARDING WHEN
THE WESTWARD ACCELERATION BEGINS, WITH THE GDMI AND HCCA MOVING
INITIALLY SLOWER THAN THE GLOBAL MODELS. THE NHC TRACK FORECAST HAS
BEEN SLOWED DOWN SLIGHTLY IN THE SHORT TERM, AND TRENDS TOWARD THE
HCCA AND GDMI AIDS.
ENVIRONMENTAL CONDITIONS REMAIN GENERALLY FAVORABLE FOR
STRENGTHENING, WITH WARM SEA SURFACE TEMPERATURES AND PLENTY OF
MID-LEVEL MOISTURE. THE ONLY INHIBITING FACTOR HAS BEEN THE WIND
SHEAR THAT HAS KEPT RACHEL'S STRENGTHENING RATE MORE GRADUAL TO
STEADY. ALTHOUGH THE WIND SHEAR HAD BEEN FORECAST TO LESSEN, IT HAS
NOT DONE SO, AND THE LATEST SHIPS FORECAST NOW KEEPS THE SHEAR
MODERATE OVER THE NEXT TWO DAYS OR SO. GIVEN THE CURRENT STRUCTURE,
THE NHC FORECAST INDICATES CONTINUED STRENGTHENING FOR THE NEXT DAY
OR SO, WHICH LIES ABOVE THE MODEL GUIDANCE. IN ABOUT 2-3 DAYS, WIND
SHEAR IS FORECAST TO DECREASE THOUGH THE HURRICANE SHOULD ENCOUNTER
DRIER MID-LEVEL AIR WHILE THE SYSTEM MOVES ALMOST PARALLEL TO THE
27C ISOTHERM. THESE FACTORS SHOULD CAUSE A WEAKENING TREND BUT HOW
FAST THAT WEAKENING OCCURS WILL BE HIGHLY DEPENDENT ON THE STRUCTURE
OF THE SYSTEM. ADDITIONALLY, WITH WEAK SHEAR AND THE HURRICANE
PARALLELING THE 27C ISOTHERM, THE STRUCTURE CAN SOMETIMES BECOME
ANNULAR, MODERATING THE WEAKENING RATE. THE LATEST NHC INTENSITY
FORECAST TRENDS BACK TOWARD THE HCCA INTENSITY AID DURING THE LATTER
PART OF THE FORECAST PERIOD WITH GRADUAL WEAKENING, ALTHOUGH THERE
REMAINS UNCERTAINTY AT THAT TIME RANGE.
FORECAST POSITIONS AND MAX WINDS
INIT 01/1500Z 19.6N 109.6W 90 KT 105 MPH
12H 02/0000Z 19.7N 110.1W 95 KT 110 MPH
24H 02/1200Z 19.8N 110.8W 100 KT 115 MPH
36H 03/0000Z 20.0N 111.5W 105 KT 120 MPH
48H 03/1200Z 20.1N 112.5W 100 KT 115 MPH
60H 04/0000Z 20.3N 113.6W 95 KT 110 MPH
72H 04/1200Z 20.4N 114.7W 90 KT 105 MPH
96H 05/1200Z 20.5N 117.2W 85 KT 100 MPH
120H 06/1200Z 20.6N 120.3W 80 KT 90 MPH
FORECASTER KELLY
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