Tropical Storm Co-May (11W/Emong) – Tropical Cyclone Advisory #6: 0000 UTC 25 July 2025

Co-May weakening rapidly over the mountainous terrain of Luzon.

Author

Will Weaver
July 24, 2025

…Co-May weakening rapidly over the mountainous terrain of Luzon…

Himawari-9 visible satellite image (Weathernerds)

Current storm information:

  • Position: 17.3°N 120.8°E

  • Movement: NE at 10 knots (20 km/h)

  • Intensity: 45 knots (85 km/h)

  • Central pressure: 990 hPa

Trend:

  • Continued rapid weakening is forecast during the next 24 hours.

Watches and warnings:

PAGASA wind signal map (click to enlarge)

  • TCWS #3 (Philippines): Ilocos Norte, northwestern Cagayan, Ilocos Sur, Apayao, Abra, western Kalinga, western Mountain Province, northern La Union, northwestern Benguet

  • TCWS #2 (Philippines): Batanes Islands, Babuyan Islands, central and eastern Cagayan, eastern Kalinga, eastern Mountain Province, Ifugao, southern La Union, southern Benguet, northern and central Nueva Vizcaya, northern and western Isabela, far northwestern Quirino, far northwestern Pangasinan 

  • TCWS #1 (Philippines): The rest of Pangasinan, southeastern Isabela, the rest of Quirino, northern Aurora, northern Zambales, northern Tarlac, Nueva Ecija

Hazards affecting land:

  • An enormous amount of rain has fallen on portions of northern and western Luzon, and Co-May is expected to exacerbate this situation both directly and through enhancement of the monsoon trough. An additional 200 to 250 mm of rainfall is possible over western coastal areas of northern and central Luzon through Saturday. This rainfall is expected to contribute to widespread, life-threatening flooding in vulnerable areas. For additional information, including rainfall and flood warnings, refer to Weather Advisories and Severe Weather Bulletins from PAGASA or products from your local weather office.

Discussion:

Himawari-9 infrared satellite image (Weathernerds)

Co-May made landfall in Ilocos Sur a couple of hours ago. The system is sending mixed signals, to the point that it’s confusing some of the agencies. Co-May’s circulation appears to have decoupled, with its robust mid-level circulation centered just off the coast of Ilocos Norte while the low-level center is moving inland over the mountains. The biggest hint that the circulation off the coast is the mid-level circulation is that convective cloud tops have warmed dramatically over water despite low shear and very warm SSTs. The convective structure has become somewhat formless with the only banding located to the south and west of the surface center. CIMSS D-PRINT estimates suggest that Co-May has weakened significantly since landfall, and the intensity is lowered to 45 kts.

There are no changes to the forecast. Co-May should emerge over water near the Babuyan Islands during the next 12 hours or so, and continued rapid weakening is expected before then. Once Co-May is back over water, the weakening should slow somewhat as the environment will briefly be somewhat favorable with warm SSTs and low to moderate shear, but by tomorrow the shear should increase rapidly and Co-May’s circulation should become stretched out within the monsoon gyre. Although the JMA forecast (which is initialized from the wrong location so take it with a grain of salt) shows forecast points beyond 48 hours, it is likely that Co-May will dissipate within the monsoon gyre sooner than that.

Forecast positions and maximum winds

  • 00 hrs: 17.3°N 120.8°E – 45 kts inland

  • 12 hrs: 19.5°N 121.5°E – 35 kts over water

  • 24 hrs: 24.4°N 125.5°E – 30 kts

  • 48 hrs: 27.0°N 127.5°E – 25 kts Post-tropical/remnant low

  • 72 hrs: Dissipated

JMA forecast map. The initial position is too far to the northwest but this track is close enough.