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Curious cloud arc southeast of Hawai`i

By Scott Bachmeier •

GOES-18 Nighttime Microphysics RGB + daytime True Color RGB images, from 1201 UTC on 30 May to 0001 UTC on 31 May [click to play MP4 animation]

5-minute CONUS Sector GOES-18 (GOES-West) Nighttime Microphysics RGB + daytime True Color RGB images from the CSPP GeoSphere site (above) revealed a curious cloud arc located southeast of the Big Island of Hawai`i (near 150 W longitude) on 30 May 2026. The fact that the typical westward transport of marine boundary layer stratocumulus clouds seemed to abruptly halt to the west of that cloud arc caused this blog post author to immediately wonder “What the heck is this?” — and assign it to the aptly-named “What the heck is this?” blog category of seemingly unexplainable meteorological phenomena.

GOES-18 Infrared Window images, from 1136 UTC on 30 May to 0001 UTC on 31 May [click to play MP4 animation]

GOES-18 Infrared Window images (above) and Visible images (below) included plots of surface analyses every 6 hours — which depicted a broad inverted trough over the area, although the position and orientation/shape of the analyzed trough axis did not match that of the actual cloud arc feature (those tropical surface analyses were produced by multiple collaborating agencies; surface analyses from NWS Honolulu also showed a trough axis near 150 W longitude).

GOES-18 Visible images, from 1531 UTC on 30 May to 0001 UTC on 31 May [click to play MP4 animation]

GOES-18 Visible, Infrared Window and Cloud Top Height derived product images at 1801 UTC on 30 May [click to enlarge]

In a toggle between GOES-18 Visible, Infrared Window and Cloud Top Height images at 1801 UTC (above), the infrared brightness temperatures of the leading edge of the cloud arc were around +10C, with Cloud Top Height values generally in the 9500-10000 ft range. According to a plot of 1200 UTC rawinsonde data from Hilo (below), those temperature and height values were near the top of the trade wind inversion.

Plot of rawinsonde data from Hilo at 1200 UTC on 30 May [click to enlarge]

Categories: GOES-18, Red-Green-Blue (RGB) images, Tropical, What the heck is this?