Tropical Storm Krosa (#12W) – Tropical Cyclone Advisory #5: 1200 UTC 25 July 2025

…Krosa stubbornly continues to strengthen despite extremely hostile environmental conditions… …Not expected to be a threat to any populated land areas…

Discussion:

Krosa is a very resilient system. Despite continuing to be pummeled by strong northwesterly shear associated with the large monsoon gyre over the East China Sea, the system has managed to develop a solid central dense overcast feature with extremely cold cloud tops (as cold as -90°C). The circulation center is quite well defined and is easily discernible on both scatterometer data and microwave satellite imagery. 89GHz microwave imagery even suggests hints of a partial eyewall feature forming, although this feature is displaced to the south of the center due to the aforementioned shear. Although Krosa’s sheared appearance is leading to relatively unimpressive Dvorak-based estimates, the scatterometer data suggests the tropical storm’s winds have increased to 45 kts.

Despite the highly unfavorable environment Krosa is currently in, it appears likely that Krosa will continue to slowly strengthen during the next couple of days as it moves almost due north under the influence of strong monsoonal flow and subtropical ridging to the northeast. As the monsoon gyre over the East China Sea breaks down and Krosa gains latitude, the shear affecting it should decrease, although dry air will likely prevent a higher rate of strengthening. Toward the end of the forecast period, Krosa should gradually turn northeastward under the influence of an approaching trough and a large belt of southwesterly wind flow that is expected to form as the monsoonal pattern to the west breaks down. These factors will offset the dry air and enhance Krosa’s outflow, and Krosa is forecast to become a typhoon over the open subtropical Pacific as the forecast period ends.

Forecast positions and maximum winds

• 00 hrs: 17.5°N 143.1°E – 45 kts

• 12 hrs: 18.7°N 144.2°E – 50 kts

• 24 hrs: 20.1°N 144.9°E – 55 kts

• 48 hrs: 24.3°N 145.7°E – 55 kts

• 72 hrs: 27.6°N 145.8°E – 55 kts

• 96 hrs: 29.3°N 146.9°E – 60 kts

• 120 hrs: 31.3°N 150.3°E – 65 kts