Tropical Storm Co-May (11W) – Tropical Cyclone Advisory #12: 0000 UTC 29 July 2025

…Co-May becomes a tropical storm yet again…

Discussion:

Co-May’s circulation has become better defined during the past few hours, and convection has also increased over and to the west of the center. However, the system is still struggling with dry air entrainment, and there is a substantial tongue of dry air wrapping into the center from the south and east. Despite the dry air, radar and microwave satellite imagery suggest the system is much better organized now, and scatterometer data and surface observations suggest it is producing winds of 30 to 35 kts again, so the intensity is increased back to 35 kts.

Co-May has been moving fairly slowly west-northwestward as steering currents collapse due to the breakdown of the monsoonal circulation it is embedded in, and surface observations indicate that some weak ridging is building in to the northeast. This ridging should cause Co-May to turn more toward the northwest later today. The environment appears to be marginally favorable, with modestly warm SSTs and low shear being offset by dry air, and Co-May will likely only strengthen slightly before making landfall in the Shanghai area on Wednesday. After landfall, Co-May should gradually turn northward, then northeastward as it rounds the periphery of the ridge. Although it will be spending quite a bit of time over land, it will likely emerge over the Yellow Sea as a tropical depression on Sunday.

Forecast positions and maximum winds

• 00 hrs: 27.2°N 124.9°E – 35 kts

• 12 hrs: 28.5°N 123.4°E – 35 kts

• 24 hrs: 30.0°N 122.8°E – 40 kts

• 48 hrs: 32.4°N 120.0°E – 35 kts inland

• 72 hrs: 33.4°N 118.8°E – 25 kts inland

• 96 hrs: 34.6°N 119.4°E – 25 kts inland

• 120 hrs: 35.0°N 120.5°E – 25 kts over water