054
WTPZ44 KNHC 072120
TCDEP4
TROPICAL STORM IVO DISCUSSION NUMBER 5
NWS NATIONAL HURRICANE CENTER MIAMI FL EP092025
300 PM CST THU AUG 07 2025
IVO REMAINS A VERY SMALL TROPICAL CYCLONE, THOUGH AN INTENSIFYING
ONE. DEEP CENTRAL CONVECTION CONTINUES TO BURST NEAR THE CENTER,
THOUGH THE VERTICAL STRUCTURE OF THE TROPICAL STORM DOES APPEAR MORE
RAGGED WITH EVIDENCE THAT THE MID-LEVEL VORTEX IS TILTED TO THE
SOUTHWEST OF THE LOW-LEVEL CENTER. A HELPFUL METOP-B SCATTEROMETER
PASS AT 1643 UTC CAPTURED THE TINY CIRCULATION WITH A MAX WIND
RETRIEVAL OF 44 KT. ASSUMING THIS INSTRUMENT UNDERSAMPLED THE PEAK
WINDS OF THE SMALL CYCLONE, THE INITIAL INTENSITY IS BEING RAISED TO
50 KT FOR THIS ADVISORY, ALSO CLOSE TO THE LATEST OBJECTIVE ADT
ESTIMATE.
THE TROPICAL STORM CONTINUES TO MOVE QUITE QUICKLY TO THE NORTHWEST,
WITH THE MOTION ESTIMATED AT 305/18 KT. THE TRACK FORECAST REASONING
IS SIMILAR TO EARLIER, WHERE A STRONG AND EXTENSIVE MID-LEVEL RIDGE
PARKED OVER NORTHERN MEXICO SHOULD KEEP IVO MOVING QUICKLY
WEST-NORTHWESTWARD TO NORTHWESTWARD FOR THE NEXT 24 HOURS OR SO. ON
THIS FORECAST TRACK, IVO WILL SOON BEGIN PULLING AWAY FROM THE
SOUTHWESTERN COAST OF MEXICO. BY THIS WEEKEND, THE RIDGE BEGINS TO
WEAKEN SOME AND THE GUIDANCE ALSO SUGGESTS IVO WILL START TO BECOME
MORE VERTICALLY SHALLOW. A COMBINATION OF THESE INFLUENCES SHOULD
RESULT IN A WESTWARD TURN IN THE TRACK AND A SLOWDOWN IN THE FORWARD
MOTION. THE TRACK GUIDANCE FOR THIS CYCLE IS QUITE SIMILAR TO THE
PRIOR ONE, AND THE NHC TRACK FORECAST IS LARGELY AN UPDATE FROM
THE PREVIOUS ONE, BLENDING THE CONSENSUS AIDS HCCA AND TVCE.
THE INTENSITY FORECAST PRESENTS A CONUNDRUM THIS AFTERNOON. IVO HAS
A SMALL INNER CORE WIND FIELD, IS OVER WARM 29-30 C OCEAN WATERS,
AND VERTICAL WIND SHEAR AS DIAGNOSED BY SHIPS GUIDANCE IS LOW, ONLY
5-10 KT. ORDINARILY THESE VARIABLES WOULD SUGGEST THAT IVO COULD
UNDERGO A PERIOD OF RAPID INTENSIFICATION (RI), AND EC-SHIPS-RI
GUIDANCE NOW HAS A 71 PERCENT CHANCE OF A 30-KT INCREASE OVER THE
NEXT 24 H. HOWEVER, OTHER RI INDICES ARE LOWER, WITH DTOPS AT ONLY
12 PERCENT FOR THE SAME THRESHOLD. THERE IS ALSO EVIDENCE THAT IVO'S
STRUCTURE IS NOT IDEAL, WITH CURRENT VISIBLE SATELLITE IMAGERY
SUGGESTING ITS CIRCULATION IS TILTED SOUTHWEST WITH HEIGHT. THIS
VERTICAL TILT ALSO MATCHES THE STRUCTURE SEEN IN THE MOST RECENT
HAFS-A/B MODEL GRIDS. THIS MAY EXPLAIN WHY THE REGIONAL-HURRICANE
MODELS ARE LESS AGGRESSIVE WITH IVO'S INTENSIFICATION THAN SHIPS,
AND ONLY HAFS-B BRIEFLY MAKES IVO A HURRICANE. THUS THE NHC
INTENSITY FORECAST IS NOT AS AGGRESSIVE AS THE LATEST SHIPS
GUIDANCE, ONLY TAKING IVO TO A 70 KT HURRICANE IN 24 HOURS.
THEREAFTER, THE STORM WILL CROSS A SHARP SEA-SURFACE TEMPERATURE
GRADIENT, WHICH SHOULD LEAD TO WEAKENING AFTER 24 HOURS. LIKE THE
PREVIOUS FORECAST, IVO WILL LIKELY LOSE ITS ORGANIZED DEEP
CONVECTION WEST OF BAJA CALIFORNIA IN ABOUT 72 HOURS, WHERE THE
LATEST FORECAST SHOWS IT BECOMING A POST-TROPICAL REMNANT LOW. THE
NHC INTENSITY FORECAST IS A LITTLE ABOVE THE RELIABLE HCCA AID, BUT
IS LOWER THAN BOTH SHIPS AND LGEM AIDS.
GIVEN THE SMALL RADIUS OF TROPICAL-STORM-FORCE WINDS ASSOCIATED WITH
IVO, THESE WINDS ARE EXPECTED TO REMAIN OFFSHORE AS IT BEGINS TO
MOVE AWAY FROM MEXICO BY TONIGHT. HOWEVER, HEAVY RAIN AND ROUGH SURF
ARE LIKELY TO OCCUR ALONG PORTIONS OF THE SOUTHWEST COAST OF MEXICO
DURING THE NEXT DAY OR SO. OUTER BANDS OF IVO ARE EXPECTED TO
PRODUCE LOCALLY HEAVY RAINFALL IN PORTIONS OF THE MEXICAN STATES OF
GUERRERO, MICHOACAN DE OCAMPO AND COLIMA THROUGH FRIDAY WHERE FLASH
FLOODING IS POSSIBLE.
FORECAST POSITIONS AND MAX WINDS
INIT 07/2100Z 18.8N 105.8W 50 KT 60 MPH
12H 08/0600Z 20.1N 108.2W 60 KT 70 MPH
24H 08/1800Z 21.1N 110.9W 70 KT 80 MPH
36H 09/0600Z 21.5N 112.8W 65 KT 75 MPH
48H 09/1800Z 21.6N 114.1W 55 KT 65 MPH
60H 10/0600Z 21.7N 115.8W 40 KT 45 MPH
72H 10/1800Z 21.9N 117.5W 30 KT 35 MPH...POST-TROP/REMNT LOW
96H 11/1800Z 22.5N 121.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 12/1800Z...DISSIPATED
FORECASTER PAPIN
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