Tropical Depression — Rota, Guam

2025-07-24 to 2025-07-25 · Rota, Guam

Event narrative

Tropical Storm Krosa (12W) produced peripheral impacts to the Marianas during the period of July 24-27 as the enter kept west of the Marianas, with no fatalities or injuries reported, and only minimal damage to shade structures, signage, and a few down trees along public beaches of Saipan, caused by storm surge/tide. Krosa developed within a west-ward moving surface trough in northern Chuuk State as monitored as Invest 98W by the Joint Typhoon Warning Center on July 21st. Invest 98W passed over Guam during the overnight hours of July 23-24 and would become Tropical Depression 12W west of Guam. TD 12W would continue to intensify into a tropical storm early on July 25th and would maintain a northerly heading, keeping just west of the Marianas island chain. The northern islands of Agrihan, Alamagan, and Pagan are sparsely populated and have no weather observations so weather data if very limited. Based on satellite-derived and TC forecast wind radii, tropical storm winds did encompass the northern islands on July 26-27, possibly reaching up to around 60 mph. Estimated max winds near the center was 65 mph. In the wake of Krosa, a monsoon surge wrapped around the southern and eastern sides of Krosa, prolonging gusty and showery conditions. Krosa would eventually become a typhoon at 7AM ChST July 28th as it left WFO Guam's area of responsibility. Peak storm surge estimate available was at Saipan and was roughly estimated to be around 2 to 3 feet, based on subtracting the predicted astronomical tide height of 1 foot (referenced to mean sea level) from the estimated run-up line height that was based on photos taken after the event. The minimum sea-level pressure recorded over land was 1006 mb via the ASOS on Saipan. Peak rainfall of 4.06 inches was also recorded at Saipan over a 48 hour period. The ASOS on Saipan recorded a peak wind of 19 kts (22 mph) with a peak gust of 34 kts (39 mph). Similar conditions were experienced at nearby Tinian but observations are limited as the airport where obs are taken is part time and a wind sock is used. Rota observations are limited for the same reasons as Tinian. From the observation taken at the airport, peak winds recorded was 16 kt (18 mph) with a peak gust of 19 kt (22 mph).

Wider weather episode

Tropical Storm Krosa (12W) produced peripheral impacts to the Marianas during the period of July 24-27 as the center kept west of the Marianas, with no fatalities or injuries reported, and only minimal damage to shade structures, signage, and a few down trees along public beaches of Saipan, caused by storm surge/tide. Krosa developed within a west-ward moving surface trough in northern Chuuk State as monitored as Invest 98W by the Joint Typhoon Warning Center on July 21st. Invest 98W passed over Guam during the overnight hours of July 23-24 and would become Tropical Depression 12W west of Guam. TD 12W would continue to intensify into a tropical storm early on July 25th and would maintain a northerly heading, keeping just west of the Marianas island chain. In the wake of Krosa, a monsoon surge wrapped around the southern and eastern sides of Krosa. Krosa would eventually become a typhoon at 7AM ChST July 28th as it left WFO Guam's area of responsibility. The minimum sea-level pressure recorded over land was 1006 mb via the ASOS on Saipan. Peak rainfall of 4.06 inches was also recorded at Saipan over a 48 hour period. The ASOS on Saipan recorded a peak wind of 19 kts (22 mph) with a peak gust of 34 kts (39 mph). Peak storm surge estimate available was at Saipan and was roughly estimated to be around 2 to 3 feet, based on subtracting the predicted astronomical tide height of 1 foot (referenced to mean sea level) from the estimated run-up line height that was based on photos taken after the event.

Source: NOAA Storm Events Database, event_id 1290130. Narrative written by the NWS forecast office that issued the report.