Super Typhoon Mawar: An Observational Analysis of Its Evolution and Impacts to Guam

Super Typhoon Mawar (02W, May 2023) was the strongest typhoon to strike the island of Guam in nearly 21 years. After developing 600 miles to the south-southeast of Guam on 20 May, Mawar steadily intensified into a super typhoon (winds 150 mph or greater) on 23 May. An eyewall replacement cycle (ERC) weakened Mawar to a 115 mph category 4 typhoon as it approached northern Guam. However, within a day of landfall over northern Guam, Mawar rapidly intensified to a peak satellite-estimated intensity of 185 mph on 26 May.

Mawar’s slow passage over Guam led to prolonged torrential rains with much of the island receiving nearly 2 feet of rain flooding . Wind damage varied significantly from north to south across the 30mi long island with devastation in the north consistent with category 4 typhoon winds and damage in the south consistent with category 1-2 typhoon winds. Concrete structures fared well, with the exception of wind-driven water intrusion or flooding, while many non-concrete structures were demolished.

Of the National Weather Service (NWS) Guam meteorologists that maintained operations behind shuttered doors for more than 36 hours, only one had prior experience working during a significant tropical cyclone. For most of the staff, this was their first career tropical cyclone experience. The lead up to and passage of Mawar saw an incredible display of teamwork and communication among office staff that led to a clear and steady message to the public and decision makers. NWS Guam relied heavily on Facebook Live sessions to provide people with latest typhoon information as well as giving viewers an opportunity to ask questions and receive quick feedback.

NWS Guam saw a number of additional firsts with Mawar: it’s first issuance of the Extreme Wind Warning (EWW), which was actually added to the list of official text products for NWS Guam just one month prior; an increased reliance on the low-latency Direct Broadcast Low Earth Orbit (LEO) satellite imagery, courtesy the University of Wisconsin Cooperative Institute for Meteorological Satellite Studies (CIMSS); the debut of the National Weather Service’s new Post Storm Report (PSH) format and web-based data files; and a novel collaboration with the University of Guam Drone Corps to provide very high resolution orthomosaic images of various areas of Guam to assess coastal high water marks and vegetative and structural damage in some of the worst-hit, and hard to reach areas of Guam.