877
WTPZ42 KNHC 220843
TCDEP2
TROPICAL STORM NORMA DISCUSSION NUMBER 19
NWS NATIONAL HURRICANE CENTER MIAMI FL EP172023
300 AM MDT SUN OCT 22 2023
CONVECTIVE BURSTS HAVE REDEVELOPED OVER THE NORTHEASTERN POTION OF
NORMA'S CIRCULATION, BUT THE CENTER REMAINS EXPOSED DUE TO STRONG
SOUTHWESTERLY SHEAR. OVERNIGHT SHORTWAVE INFRARED SATELLITE
IMAGERY AND A COUPLE OF FORTUITOUS ASCAT OVERPASS SHOWED THAT
THE CENTER OF NORMA EXITED THE EAST COAST OF THE BAJA CALIFORNIA
PENINSULA A LITTLE FARTHER NORTH THAN PREVIOUSLY ESTIMATED.
THEREFORE, THE INITIAL POSITION FOR THIS ADVISORY HAS BEEN ADJUSTED
NORTHWARD ACCORDINGLY. PEAK WINDS IN THE SCATTEROMETER PASSES WERE
AROUND 45 KT, BUT OWING TO THAT INSTRUMENT'S TYPICAL LOW BIAS THE
INITIAL INTENSITY HAS ONLY BEEN LOWERED TO 50 KT.
SINCE MOST OF THE NORMA'S CIRCULATION IS FORECAST TO REMAIN OVER
THE GULF OF CALIFORNIA WATERS TODAY, LITTLE CHANGE IN STRENGTH IS
EXPECTED IN THE SHORT TERM. ONCE NORMA MOVES INLAND OVER MAINLAND
MEXICO, RAPID WEAKENING AND DISSIPATION OVER THE HIGH TERRAIN IS
EXPECTED.
THE INITIAL MOTION ESTIMATE IS NORTH-NORTHEASTWARD OR 25 DEGREES AT
6 KT. MOST OF THE DYNAMICAL MODEL GUIDANCE INDICATES THAT NORMA WILL
TURN NORTHEAST, AND THEN EAST-NORTHEAST DURING THE NEXT 12 TO 24
HOURS, AND THE OFFICIAL FORECAST FOLLOWS THIS SCENARIO. THERE IS
FAIRLY SIGNIFICANT SHORT-TERM SPREAD IN THE GUIDANCE WITH THE GFS
TAKING THE SYSTEM MORE EASTWARD, WHILE THE HWRF AND ECMWF MODELS
DEPICTED A MORE NORTHEASTWARD MOTION THROUGH LANDFALL. THE NHC
TRACK HAS BEEN SHIFTED SIGNIFICANTLY NORTH OF THE PREVIOUS ADVISORY
DUE TO THE MORE NORTHWARD INITIAL POSITION, AND THE NEW TRACK LIES
NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE. IT SHOULD BE NOTED THAT
ALTHOUGH THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY ON EXACTLY
WHERE AND WHEN THE CENTER OF NORMA WILL CROSS THE COAST OF MAINLAND
MEXICO, GUSTY WINDS AND HEAVY RAINFALL ARE EXPECTED TO SPREAD
ONSHORE ALONG MUCH OF THE COAST OF THE MEXICAN STATE OF SINALOA
THROUGH TONIGHT.
KEY MESSAGES:
1. HEAVY RAINS FROM NORMA WILL CONTINUE TO IMPACT SINALOA INTO
MONDAY. RAINFALL WILL CONTINUE TO DIMINISH ACROSS THE SOUTHERN
PORTIONS OF BAJA CALIFORNIA SUR EARLY THIS MORNING. THIS RAINFALL
WILL PRODUCE FLASH AND URBAN FLOODING, ALONG WITH MUDSLIDES IN AREAS
OF HIGHER TERRAIN.
2. TROPICAL STORM CONDITIONS WILL CONTINUE THROUGH THIS AFTERNOON
WITHIN PORTIONS OF THE TROPICAL STORM WARNING AREA OVER THE SOUTHERN
BAJA CALIFORNIA PENINSULA.
3. TROPICAL STORM CONDITIONS ARE EXPECTED TO SPREAD ONSHORE ALONG
PORTIONS OF THE WEST COAST OF MAINLAND MEXICO WITHIN THE TROPICAL
STORM WARNING AREA THROUGH TONIGHT.
FORECAST POSITIONS AND MAX WINDS
INIT 22/0900Z 24.5N 109.8W 50 KT 60 MPH
12H 22/1800Z 25.0N 109.2W 50 KT 60 MPH
24H 23/0600Z 25.3N 108.5W 45 KT 50 MPH...INLAND
36H 23/1800Z 25.7N 107.6W 25 KT 30 MPH...POST-TROP/REMNT LOW
48H 24/0600Z...DISSIPATED
FORECASTER BROWN
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