808
WTPZ43 KNHC 292048
TCDEP3
TROPICAL STORM RACHEL DISCUSSION NUMBER 11
NWS NATIONAL HURRICANE CENTER MIAMI FL EP182026
300 PM CST TUE SEP 29 2026
THERE HAS BEEN A WEALTH OF DATA TO PARSE THROUGH THIS AFTERNOON WITH
RACHEL. ON SATELLITE IMAGERY, RACHEL IS EXHIBITING A LARGE
CONVECTIVE BURST WITH CLOUD TOPS BELOW -85 C, THOUGH THIS BURST IS
STILL CENTERED A LITTLE SOUTH OF THE CENTER FIXES PROVIDED BY THE
NOAA P-3 AIRCRAFT THAT CONDUCTED A RESEARCH MISSION INTO THE STORM.
THE PEAK 700-MB FLIGHT LEVEL WINDS FROM THE MISSION WERE 66 KT. IN
ADDITION, THERE WAS A DROPSONDE LAUNCHED IN THE RADIUS OF MAXIMUM
WIND ON ITS EAST SIDE THAT HAD 500 M AVERAGE OF 75 KT, WHICH USING
A TYPICAL REDUCTION FACTOR YIELDS 60 KT. FURTHERMORE, THERE WAS A
UNCREWED AIRCRAFT SYSTEM (UAS) THAT WAS LAUNCHED IN THE SAME AREA IN
THE BOUNDARY LAYER, FINDING 975-MB WINDS ALSO UP TO 75 KT. AN
EXPERIMENTAL REDUCTION FACTOR DEVELOPED BY CIRA INDICATED THIS VALUE
TRANSLATES TO A 10-METER SUSTAINED WIND OF 63 KT. ALL OF THE ABOVE
DATA SUGGESTS THAT RACHEL IS NEARLY A HURRICANE, AND THE INITIAL
INTENSITY IS SET AT 60 KT THIS ADVISORY. A 1620 UTC ASCAT-B PASS, IN
ADDITION TO THE AIRCRAFT DATA, WERE BOTH USEFUL TO ADJUST THE 34-
AND 50-KT RADII THIS AFTERNOON.
RACHEL CONTINUES TO MOVE OFF TO THE NORTHWEST, WITH AIRCRAFT FIXES
INDICATING A MOTION OF 305 DEGREES AT 12 KT. A MID-LEVEL RIDGE
LOCATED OVER CENTRAL MEXICO IS EXPECTED TO STEER THE TROPICAL
CYCLONE IN THAT SAME DIRECTION OVER THE NEXT 12-24 H. HOWEVER, AN
UPPER-LEVEL CUTOFF LOW MOVING ACROSS THE FOUR CORNERS REGION OF THE
SOUTHWESTERN UNITED STATES WILL SOON ERODE THIS RIDGE, LEADING TO A
SIGNIFICANT SLOWDOWN IN RACHEL'S MOTION. AFTER 48 H, ANOTHER
MID-LEVEL RIDGE BEGINS TO BUILD IN OVER CALIFORNIA AND NEVADA BEHIND
THIS CUTOFF LOW AS IT EJECTS INTO THE CENTRAL PLAINS. THE NET EFFECT
OF THIS SYNOPTIC PATTERN IS RACHEL SHOULD THEN TURN MORE WESTWARD,
BUT STILL AT A SLOW FORWARD MOTION. SOME OF THE RELIABLE TRACK AIDS
HAVE MADE A SOUTHWARD SHIFT IN RACHEL'S TRACK THIS AFTERNOON, AND
THE LATEST NHC TRACK FORECAST HAS BEEN SHIFTED IN THAT DIRECTION,
BLENDING THE HFIP CORRECTED CONSENSUS APPROACH (HCCA), THE GOOGLE
DEEPMIND ENSEMBLE MEAN (GDMI), AND THEIR NEW EXPERIMENTAL MODEL
(WN3I).
SHEAR ANALYSIS FROM UW-CIMSS INDICATES THAT THE NORTHEASTERLY SHEAR
THAT HAD BEEN AFFECTING RACHEL IS STARTING TO DECREASE, AND BOTH THE
EC- AND GFS-BASED SHIPS GUIDANCE SHOW THIS LOWERING BELOW 15 KT IN
24 H. IN ADDITION, THE LATEST FORECAST TRACK BRINGS RACHEL INITIALLY
TO THE NORTH OF THE COOL WAKE LEFT BEHIND BY POLO, WITH NEARBY OCEAN
DRIFTERS STILL SHOWING SEA-SURFACE TEMPERATURES (SSTS) IN THE 29-30
C RANGE STILL. THUS AS THE SHEAR DECREASES, AND ASSUMING RACHEL'S
CORE IS BECOMING MORE VERTICALLY ALIGNED, THE SHORT-TERM INTENSITY
HAS BEEN RAISED AND NOW SHOWS A PERIOD OF RAPID INTENSIFICATION FROM
24-48 H, MAKING IT A 105 KT MAJOR HURRICANE AT THE END OF THAT TIME
FRAME. AFTER THAT TIME, AS RACHEL TURNS WESTWARD, IT WILL FINALLY
PASS OVER POLO'S COOL WAKE, WHERE ANOTHER DRIFTER IN THAT VICINITY
SHOWING SSTS MUCH LOWER, IN THE 26-27 C RANGE, AND THAT COMBINED
WITH RACHEL'S SLOW MOTION WILL LIKELY LEAD TO WEAKENING IN 60-96 H.
THE LATEST NHC INTENSITY FORECAST REMAINS ON THE UPPER-END OF THE
GUIDANCE, CLOSEST TO HCCA THROUGH 48 H, BUT THEN FALLS BACK CLOSER
TO THE GUIDANCE MEAN IN 72-120 H.
KEY MESSAGES:
1. ALTHOUGH THE CORE OF RACHEL IS FORECAST TO REMAIN OFFSHORE OF
MEXICO, TROPICAL-STORM-FORCE WINDS ARE EXPECTED ALONG A PORTION OF
THE COAST OF SOUTHWESTERN MEXICO IN THE TROPICAL STORM WARNING AREA
TODAY OR TONIGHT. TROPICAL STORM CONDITIONS ARE POSSIBLE IN THE
WATCH AREA TONIGHT OR ON WEDNESDAY.
2. OUTER BANDS FROM RACHEL WILL BRING LOCALLY HEAVY RAINFALL TO
PORTIONS OF COASTAL SOUTHWEST MEXICO THROUGH THURSDAY. THIS RAINFALL
MAY PRODUCE LIFE-THREATENING FLOODING AND MUDSLIDES, ESPECIALLY IN
AREAS OF STEEP TERRAIN.
3. LARGE WAVES COULD PRODUCE LIFE-THREATENING SURF AND RIP CURRENT
CONDITIONS ALONG PORTIONS OF THE SOUTHWESTERN COAST OF MEXICO DURING
THE NEXT SEVERAL DAYS.
FORECAST POSITIONS AND MAX WINDS
INIT 29/2100Z 16.0N 105.7W 60 KT 70 MPH
12H 30/0600Z 17.3N 107.0W 70 KT 80 MPH
24H 30/1800Z 18.2N 108.0W 85 KT 100 MPH
36H 01/0600Z 19.0N 108.9W 100 KT 115 MPH
48H 01/1800Z 19.4N 109.5W 105 KT 120 MPH
60H 02/0600Z 19.6N 110.3W 100 KT 115 MPH
72H 02/1800Z 19.8N 111.1W 90 KT 105 MPH
96H 03/1800Z 20.2N 112.9W 80 KT 90 MPH
120H 04/1800Z 20.5N 115.0W 85 KT 100 MPH
FORECASTER PAPIN
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