Western Alaska Floods
By J. Torres (CIRA), C. Dierking (GINA) and J. Delamere (GINA).
In Early October 2025, Typhoon Halong developed in the north Philippine Sea, skirted near Japan and eventually trekked eastward into the north Pacific Ocean. The storm became post-tropical, but continued to travel eastward through the north Pacific, then traversed through the Aleutian Islands and made landfall in western Alaska. The Ocean Prediction Center (OPC) surface analysis of the storm track can be viewed from ~00Z, 12 October 2025 to ~15Z, 13 October 2025. The synoptic-scaled system brought Alaska precipitation, hurricane-force winds and significant storm surge that led to widespread inundation, impacting the coastal communities and villages.
OPC Surface Analysis → ~00Z, 12 October 2025 to ~15Z, 13 October 2025
The strong system made landfall along the Alaskan coastline during the early morning hours of 12 October 2025. Air temperatures were in the 30’s and 40’s (in degrees Fahrenheit) while 80+ mph wind gusts were also reported. The prolonged, intense winds aided in the storm surge that inundated the coastal communities. In the AWIPS animation below, the surface observations can be seen overlaid onto the 375-m VIIRS 11.5 µm infrared imagery. The imagery also observes the central low pressure system that moves to the northeast as it approaches the coastline.
Surface Observations overlaid onto VIIRS 11.5 µm from 12-16Z, 12 October 2025
South of the central low pressure system, the GCOM AMSR-2 Sea Surface Winds product observed the wind speeds over the Bering Sea near Nunivak Island and the villages of Kipnuk, AK and Kwigillingok, AK. The sea surface winds were seen from 41 to 60 plus knots (i.e., 47 to 70 plus mph, depicted in orange, dark orange, and red colors) and located south and west of where Kipnuk and Kwigillingok reside. Note, one of the limitations of the AMSR-2 product is that it does not provide data within ~50 km (~31 miles) of land or ice. At this timestamp, the strongest winds of the system would have been observed along the coastline, meaning the most intense winds were not well represented here. The product exhibits a 6-km spatial resolution in AWIPS.
AMSR-2 Sea Surface Winds overland onto VIIRS 11.5 µm at ~1317Z, 12 October 2025
After the system passed, widespread flooding could be seen along the coastline, specifically from Kwigillingok, AK to Kipnuk, AK, and up north to Hooper Bay, AK. The VIIRS Day Land Cloud RGB, at 375-m, shows a daytime before and after image comparison of the new flood extent. Along the coastline, a mix of dark green and dark blue colors indicate new areas of marshy vegetation and inundation. Refer to the inundation within the white boxes.
VIIRS Day Land Cloud RGB –> Before (October 10th) and After (October 12th)
Zooming into the southernmost white box, where Kipnuk and Kwigillingok reside, the finer details of the inundation can be seen at high resolution. A Google map is also provided to help viewers locate the Alaskan villages along the coastline.
Although clouds were scattered across the region, the VIIRS Flood Map product was also able to detect some areas of inundation from the event, seen in green to yellow to red pixels at 375-m. Clouds and cloud terrain shadows are seen in grey and dark grey colors, while land is seen in brown. The flood product can be accessed online via RealEarth and in AWIPS.
VIIRS Flood Map –> 2217Z, 12 October 2025
In addition to storm surge, heavy precipitation was also observed over western Alaska. Moisture satellite products, such as the Blended Total Precipitable Water (TPW) and the Percent of Normal TPW provided a large-scale view of ex-Typhoon Halong, which eventually reorganized and intensified, bringing a plume of moisture that led to precipitation over the region. The Blended TPW product contains microwave data from polar-orbiting satellites, infrared data from geostationary satellites and Global Positioning System (GPS) TPW data. TPW values of ~1 to 2 inches (green to red colors) can be seen over western Alaska.
Blended TPW –> 17Z, 10 October 2025 to 10Z, 13 October 2025
In complement to Blended TPW, the Percent of Normal TPW product showed the significance of the anomalous atmospheric moisture within the system. In this case, exceptionally high percent of normal values (i.e., above normal climatological values of 200% or greater) were captured within the system, seen in yellow and gray colors.
Percent of Normal TPW –> 17Z, 10 October 2025 to 10Z, 13 October 2025
Additional reports and analyses of the event can be viewed below. Refer to the following articles covering the Western Alaska Floods: Anchorage Daily News, The Conversation, and the Alaska Beacon.