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Orographic waves downwind of the Hawaiian Islands

By Scott Bachmeier •

GOES-18 Mid-level Water Vapor (6.9 µm) and Upper-level Water Vapor (6.2 µm) images, from 0601 UTC on 23 October to 0001 UTC on 24 October [click to play MP4 animation]

5-minute PACUS Sector GOES-18 (GOES-West) Mid-level Water Vapor and Upper-level Water Vapor images (above) displayed orographic waves downwind (southwest) of the Hawaiian Islands on 23 October 2025. With a ridge of high pressure north of Hawai’i (surface analyses), boundary layer flow from the northeast interacted with the topography of the island chain — generating vertically-propagating waves that were apparent in Mid-level (and to a lesser extent, even Upper-level) Water Vapor imagery (below).

GOES-18 Mid-level Water Vapor (6.9 µm) image and Topography [click to enlarge]

Northwest of the Big Island of Hawai’i, there was one Pilot Report of continuous light turbulence between the altitudes of 18000-20000 ft (below).

GOES-18 Mid-level Water Vapor (6.9 µm) image at 0001 UTC on 24 October, with a cursor sample of a Pilot Report at 0011 UTC [click to enlarge]

One item of interest was the diurnal change in thermal signatures of the Mauna Kea and Mauna Loa summits — transitioning from cooler (darker shades of blue) during the nighttime at 1201 UTC to warmer (brighter shades of yellow) during the daytime at 0001 UTC (below).

GOES-18 Mid-level Water Vapor (6.9 µm) images at 1201 UTC on 23 October and 0001 UTC on 24 October [click to enlarge]

Plots of Weighting Functions for the GOES-18 Mid-level and Upper-level Water Vapor spectral bands — derived using rawinsonde data from Hilo (PHTO) — showed the profiles of Band 08 and Band 09 weighting functions at 1200 UTC on 23 October to 0000 UTC on 24 October (below). The summits of Mauna Kea and Mauna Loa extend upward to near the 600 hPa pressure level — close to the level of strong weighting function contributions for Water Vapor spectral band 09 at each of those 2 times.

Weighting Function plots of GOES-18 Mid-level Water Vapor (6.9 µm / Band 09, cyan) and Upper-level Water Vapor (6.2 µm / Band 08, brown) spectral bands near the Big Island of Hawai`i [click to enlarge]

This diurnal variability of Mauna Kea and Mauna Loa thermal signatures in Water Vapor imagery has been discussed in previous blog posts here, here and here.

Categories: Aviation, General interpretation, GOES-18