SIO: HORACIO - Moderate Tropical Storm

[Subtrop]

97S INVEST 260213 0600 7.5S 69.4E SHEM 15 0

[cycloneye]

AN AREA OF CONVECTION (INVEST 97S) HAS PERSISTED NEAR 11.0S
74.2E, APPROXIMATELY 271 NM SOUTH-SOUTHEAST OF DIEGO GARCIA. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A CONSOLIDATING LOW LEVEL
CIRCULATION (LLC) OBSCURED BY A BROAD REGION OF FLARING CONVECTION
ESPECIALLY ON THE NORTH AND EASTERN PERIPHERY. A 170358Z ASCAT PASS
REVELS THAT THE LLC REMAINS EMBEDDED WITHIN THE MONSOON TROUGH BUT IS
BEGINNING TO CONGEAL INTO A SEPARATE CIRCULATION. THE ASCAT REVEALED
WINDS UP TO 30 KNOTS ALONG THE NORTHERN FLANK OF THE TROUGH, AND UP TO
20 KNOTS ALONG THE SOUTHERN FLANK. ENVIRONMENTAL ANALYSIS REVEALS
MODERATELY FAVORABLE CONDITIONS FOR DEVELOPMENT WITH HIGH VERTICAL WIND
SHEAR (20 TO 25KTS), WARM SEA SURFACE TEMPERATURES (28-29 C), AND GOOD
EQUATORWARD OUTFLOW. GLOBAL MODELS ARE IN AGREEMENT OF THE STEADY
DEVELOPMENT OF 97S WITH NAVGEM BEING THE MOST AGGRESSIVE DEPICTING RAPID
DEVELOPMENT. ENSEMBLES MODELS ARE ALSO IN AGREEMENT OF ITS FORMATION,
BOTH GLOBAL AND ENSEMBLE MODELS DEPICT 97S HAVING A GENERALLY SOUTH
EASTERLY TRACK OVER THE NEXT 48 HOURS. MAXIMUM SUSTAINED SURFACE WINDS
ARE ESTIMATED AT 18 TO 23 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED
TO BE NEAR 1006 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT
TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS IS LOW.
(2) NO OTHER SUSPECT AREAS.

[cycloneye]

THE AREA OF CONVECTION (INVEST 97S) PREVIOUSLY LOCATED NEAR
11.6S 74.8E IS NOW LOCATED NEAR 11.8S 74.8E, APPROXIMATELY 163 NM SOUTH
OF DIEGO GARCIA. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
DEPICTS AN ELONGATED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH DEEP
CONVECTION BUILDING NEAR THE CENTER. A PARTIAL 171556Z ASCAT-B PASS
REVEALED WINDS OF 20-25 KNOTS ON THE SOUTHERN AND WESTERN PERIPHERIES.
ENVIRONMENTAL ANALYSIS REVEALS FAVORABLE CONDITIONS FOR DEVELOPMENT WITH
LOW VERTICAL WIND SHEAR (10-15 KNOTS), MODERATE OUTFLOW ALOFT, AND WARM
SEA SURFACE TEMPERATURES (28-29 C). GLOBAL MODELS ARE IN GOOD AGREEMENT
ON STEADY DEVELOPMENT AND A SOUTH-SOUTHWESTWARD TRACK OVER THE NEXT 48
HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED AT 23 TO 28 KNOTS.
MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR 1003 MB. THE
POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL CYCLONE WITHIN
THE NEXT 24 HOURS IS UPGRADED TO MEDIUM.

[cycloneye]

A suspicious area is currently present south of the Chagos Archipelago (Diego Garcia) at approximately 11 degrees South and 75 degrees East. The risk of it developing into a tropical storm becomes moderate starting Thursday, February 19, and then significant on Friday, February 20. If it forms, this system is expected to follow a south-southwest trajectory, initially remaining far from inhabited land.

[cycloneye]

sasha_B, Hurricane2022, WaveBreaking, Teban54, this one will be another good one to track.

[Hurricane2022]

sasha_B, Hurricane2022, WaveBreaking, Teban54, this one will be another good one to track.

https://i.imgur.com/R6ufxVb.gif

Sure. I think we'll see another Category 3-4 storm wandering around before weakening while passing near the Mauritius islands.

[Hurricane2022]

[cycloneye]

HWRF and HAFS-A are very bullish and are up to cat 3.

[cycloneye]

THE AREA OF CONVECTION (INVEST 97S) PREVIOUSLY LOCATED NEAR
11.8S 74.8E IS NOW LOCATED NEAR 12.5S 76.1E, APPROXIMATELY 375 NM
SOUTHEAST OF DIEGO GARCIA. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY (EIR) DEPICTS A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) WITH PERSISTENT DEEP CONVECTION IN THE SOUTHWEST QUADRANT. A
181535Z ASCAT-B PASS REVEALS 25-30 KNOT WINDS CONSOLIDATING IN THE
NORTHERN AND SOUTHERN PERIPHERIES. ENVIRONMENTAL ANALYSIS FOR THE AREA
INDICATES A MARGINALLY FAVORABLE ENVIRONMENT FOR DEVELOPMENT WITH
MODERATE VERTICAL WIND SHEAR (15-20 KNOTS), WARM SEA SURFACE
TEMPERATURES (28-29 C), AND MODERATE POLEWARD OUTFLOW ALOFT. GLOBAL
MODELS ARE IN GOOD AGREEMENT ON A STEADY DEVELOPMENT AND A SOUTH-
SOUTHWESTWARD TRACK OVER THE NEXT 48 HOURS. MAXIMUM SUSTAINED SURFACE
WINDS ARE ESTIMATED AT 27 TO 32 KNOTS. MINIMUM SEA LEVEL PRESSURE IS
ESTIMATED TO BE NEAR 1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A
SIGNIFICANT TROPICAL CYCLONE WITHIN THE NEXT 24 HOURS REMAINS MEDIUM.

[cycloneye]

THE AREA OF CONVECTION (INVEST 97S) PREVIOUSLY LOCATED NEAR
12.5S 76.1E IS NOW LOCATED NEAR 12.9S 76.3E, APPROXIMATELY 401 NM
SOUTHEAST OF DIEGO GARCIA. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY (EIR) DEPICTS A PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER
(LLCC) LOCATED APPROXIMATELY 400 NM SOUTHEAST OF DIEGO GARCIA. DEEP
CONVECTION HAS BEEN PATCHY WITH LIMITED COVERAGE, PRIMARILY CONFINED
SOUTH AND WEST OF THE CENTER DUE TO NORTHEASTERLY WIND SHEAR. WHILE
THE VORTEX REMAINS VERTICALLY TILTED DUE TO THIS SHEAR, THE LLCC HAS
BECOME BETTER DEFINED AND MORE SYMMETRIC IN RECENT HOURS. AN 182230Z
SSMIS MICROWAVE IMAGE REVEALED TIGHTLY COILED LOW-LEVEL CLOUD BANDS
AROUND THE LLCC. AN EARLIER 181611Z ASCAT PASS SHOWED 25-30 KNOT WIND
BELTS TO THE NORTH AND SOUTH OF THE LLCC, THOUGH THE MAXIMUM WINDS
REMAINED SOMEWHAT DISTANT (ABOUT 80 NM) FROM THE CENTER, INDICATING
THAT AN ORGANIZED INNER CORE WIND FIELD HAS NOT YET DEVELOPED. THE
ENVIRONMENT IS GENERALLY FAVORABLE FOR DEVELOPMENT WITH WARM SEA
SURFACE TEMPERATURES (28-29 DEGREES CELSIUS), MODERATE POLEWARD
OUTFLOW ALOFT, AND A REGION OF DEEP MOISTURE ENCOMPASSING THE LLCC.
MODERATE VERTICAL WIND SHEAR (15-20 KNOTS) IS THE PRIMARY LIMITING
FACTOR SHORT-TERM. AS THE SYSTEM BEGINS TO MOVE SOUTHWARD, IT WILL
ENTER A REGION OF LIGHTER VERTICAL SHEAR OVER THE NEXT 24 HOURS. WITH
THE WELL-DEFINED LLCC AS A FOUNDATION, THIS IS EXPECTED TO ALLOW THE
VORTEX TO BECOME MORE VERTICALLY ALIGNED, WITH DEEP CONVECTION
GRADUALLY SYMMETRIZING AROUND THE LLCC. PHYSICAL AND AI-BASED MODELS
ALIKE ARE DEVELOPING A STRONG CONSENSUS FOR SHORT-TERM DEVELOPMENT.
THE ECMWF AND GFS GLOBAL MODELS SHOW THE CYCLONE REACHING WARNING
THRESHOLD IN 24 TO 36 HOURS, THE HIGH-RESOLUTION HWRF AND HAFS-A
MODELS IN 12 TO 24 HOURS, AND THE GOOGLE DEEPMIND ENSEMBLE MEAN IN 12
TO 24 HOURS. THESE MODELS ALSO GENERALLY AGREE ON A SHORT-TERM
SOUTHWARD TRACK, BENDING SOUTH-SOUTHWESTWARD AND THEN SOUTHWESTWARD
OVER THE NEXT 48 HOURS. MAXIMUM SUSTAINED SURFACE WINDS ARE ESTIMATED
AT 27 TO 32 KNOTS. MINIMUM SEA LEVEL PRESSURE IS ESTIMATED TO BE NEAR
1000 MB. THE POTENTIAL FOR THE DEVELOPMENT OF A SIGNIFICANT TROPICAL
CYCLONE WITHIN THE NEXT 24 HOURS IS UPGRADED TO HIGH

[cycloneye]

Tropical Depression 11-2025-2026


Estimated maximum wind speeds (averaged over 10 minutes) at sea: 55 km/h.

Estimated maximum gusts at sea: 75 km/h.

Estimated pressure at the center: 1001 hPa.

Position on February 19 at 10 a.m. local time: 13.6 South / 76.6 East.

Distance from the coast of Réunion: 2355 km to the East-Northeast sector

Distance from Mayotte: 3400 km to the East sector

Movement: SOUTH-EAST, at 11 km/h.

System information:

- Tropical depression 01-20252026 is located approximately 800 km southeast of Diego Garcia.

- It will initially head south before curving its trajectory towards the southwest.

- It is expected to intensify to tropical storm status by tomorrow evening and then to tropical cyclone status by the end of the week.

[cycloneye]

Soon it will be named Horacio.

[cycloneye]

Tropical Depression 11-2025-2026


Estimated maximum wind speeds (averaged over 10 minutes) at sea: 55 km/h.

Estimated maximum gusts at sea: 75 km/h.

Estimated pressure at the center: 998 hPa.

Position on February 19 at 10 p.m. local time: 14.7 South / 76.0 East.

Distance from the coast of Réunion: 2245 km to the East-Northeast sector

Distance from Mayotte: 3330 km to the East sector

Movement: SOUTH-SOUTHWEST, at 15 km/h.

System information:

- Tropical depression 01-20252026 is located in the central part of the basin, southeast of Diego Garcia.

- It will initially head south before curving its trajectory towards the southwest.

It is expected to intensify into a tropical storm within 12 hours and then into a tropical cyclone or even stronger by the end of the week. However, significant uncertainty remains regarding the potential for further intensification.

[sasha_B]

CI 2.5 from JTWC for 19 February 1730z. Probably won't be long at all before this gets named.

Hurricane models seem pretty confident that 'future Horacio' will at least reach SSHWS Category 3. As of 12z this morning, HWRF has the cyclone at around 110 kt and 951 hPa (& potentially still intensifying) by the end of the run (+126h), while HAFS-A shows a peak of 945 hPa (and around 125 kt!) at +105h. followed by slight weakening.

[cycloneye]

Can say hello to Horacio?

[cycloneye]

JTWC up to 35kts while Meteo France remains as TD 11.

97S INVEST 260220 0000 14.8S 75.8E SHEM 35 1003

Tropical Depression 11-2025-2026


Estimated maximum wind speeds (averaged over 10 minutes) at sea: 55 km/h.

Estimated maximum gusts at sea: 75 km/h.

Estimated pressure at the center: 998 hPa.

Position on February 20 at 04:00 local time: 14.6 South / 75.9 East.

Distance from the coast of Réunion: 2240 km to the East-Northeast sector

Distance from Mayotte: 3320 km to the East sector

Movement: SOUTH-SOUTHWEST, at 7 km/h.

[StormWeather]

00Z ATCF comes in upgrading 97S/TD 11 to TC 22S by the JTWC.

I don’t have the link, so can someone provide it please?

[cycloneye]

00Z ATCF comes in upgrading 97S/TD 11 to TC 22S by the JTWC.

I don’t have the link, so can someone provide it please?

https://science.nrlmry.navy.mil/geoips/ ... ector_file

[cycloneye]

First warning from JTWC has a peak of 100kts.

[sasha_B]

00Z ATCF comes in upgrading 97S/TD 11 to TC 22S by the JTWC.

I don’t have the link, so can someone provide it please?

https://science.nrlmry.navy.mil/geoips/ ... ector_file

Oh, hey, the ATCF sector files are working again! Glad to see that - they were failing to update, or throwing "access denied" errors, for several weeks there.

Generally you can expect to wait for the JTWC to upgrade a storm to 40 kt for it to get an upgrade from an RSMC. I think this is mostly a factor of measuring 10-minute winds vs. 1-minute, although I imagine resource limitations, differences in forecasting protocols, and so forth also play a part; there are a few cases where an RSMC outside of USAmerican areas of responsibility will upgrade first, but it seems to be less common.

Subjectively, I'd put the FT at 2.5, based on PT. One could argue T3.0 based on the occasionally-continuous area of W in the band of convection but I don't know if it's consistent enough without recent MW images or scatterometry to call this a 40 kt storm. With environmental pressure set to 1008 hPa, CKZ yields a central pressure of almost exactly 1000 hPa for a 35 kt storm of this size at this latitude moving at 4 kt, more or less halfway between the most recent estimates from JTWC and MFR.