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Post-Tropical Cyclone Kiko north of Hawai’i

By Scott Bachmeier •

5-minute GOES-18 “Clean” Infrared Window (10.3 µm) images with an overlay of GLM Flash Extent Density, from 0901 UTC on 10 September to 0001 UTC on 11 September [click to play MP4 animation]

5-minute CONUS Sector GOES-18 (GOES-West) Infrared images (above) revealed the exposed low-level circulation center (LLCC) of Tropical Storm Kiko as the system continued to weaken north of the Hawaiian island of Oahu, and downgraded to a Post-Tropical Cyclone at 1500 UTC on 10 September 2025. Clusters of deep convection developed north of the LLCC after 1400 UTC, which exhibited abundant satellite-detected lightning activity. Note that the LLCC passed just to the east of a semi-stationary yellow ship report around 1301 UTC — that was the RV Kilo Moana (Maritime call sign WDA7827), an oceanographic research vessel.

A comparison of GOES-18 Infrared and Visible images (below) showed that the LLCC was more distinct in the higher spatial resolution Visible imagery — however, the LLCC eventually moved beneath the canopy of growing thunderstorms after 1900 UTC, making it impossible to further track.

5-minute GOES-18 “Clean” Infrared Window (10.3 µm, left) and “Red” Visible (0.64 µm, right) images, from 1621 UTC on 10 September to 0001 UTC on 11 September [click to play MP4 animation]

The LLCC was also very apparent in GCOM-W1 AMSR2 Microwave imagery (source) not far north-northeast of Oahu at 1150 UTC (below).

GCOM-W1 AMSR2 Microwave (36.5 GHz) image at 1150 UTC on 10 September [click to enlarge]

ASCAT surface scatterometer winds (source) from Metop-B (at 0735 UTC, when Kiko was still a Tropical Storm) and Metop-C (at 2051 UTC, about 6 hours after Kiko was downgraded to a Post-Tropical Cyclone) are shown below. The depiction of the LLCC wind field was seen to degrade during the ~13 hour period between the two ASCAT images.

ASCAT winds from Metop-B (at 0735 UTC) and Metop-C (at 2051 UTC) on 10 September

Categories: GCOM-W1, GLM, GOES-18, Lightning, Metop, Microwave, Satellite winds, Tropical cyclones