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Hurricane Force low in the southern Bering Sea

By Scott Bachmeier •

GOES-18 Air Mass RGB images, with plots of hourly surface reports [click to play animated GIF | MP4]

An anomalously-deep Hurricane Force low (surface analyses) moved eastward across the southern Bering Sea and eastern Aleutian Islands on 28 October 2022. GOES-18 (GOES-West) Air Mass RGB images (above) included plots of hourly surface reports — which showed some of the strong winds produced by this storm. Peak wind gusts included 75 knots / 86 mph at Dutch Harbor (PADU, at 0309 UTC on 29 October), 68 knots / 78 mph at Akutan (PAUT, at 0455 UTC on 29 October), 61 knots / 70 mph at St. George (PAPB, at 2140 UTC on 28 October, as heavy snow was being reported), 59  knots / 68 mph at Atka (PAAK, at 1645 UTC on 28 October) and 58 knots / 67 mph at Buoy 46073 (at 2200 UTC on 28 October). The 75 knot / 86 mph gust at Dutch Harbor and the 68 knot / 78 mph gust at Akutan occurred around the time that anomalously-strong 925 hPa winds were moving south-southeastward across the eastern Aleutian Islands (along the western and southwestern edge of the low pressure center).

The orange-to-red hues seen in the Air Mass RGB imagery indicated the presence of dry, ozone-rich stratospheric air within the upper portion of the atmospheric column (due to a lowering tropopause) — and AK-NAM40 model fields (below) suggested that the “dynamic tropopause” (taken to be the pressure of the PV1.5 surface) descended to the 600-675 hPa pressure level just south of the low pressure center.

GOES-18 Air Mass RGB images, with contours of AK-NAM40 model PV1.5 pressure [click to play animated GIF | MP4]

Gridded NUCAPS Tropopause Height (derived using Metop-B and Metop-C CrIS/ATMS data) from the NASA SPoRT site (below) showed a narrow corridor of tropopause pressures near 600 hPa (brighter red enhancement) over and just north of the eastern Aleutians at 2108 and 2200 UTC — in general agreement with the AK-NAM40 model fields.

Gridded NUCAPS Tropopause Height [click to enlarge]


GOES-18 Air Mass RGB image at 1800 UTC, with contours of AK-NAM40 model PV1.5 pressure and Baseline B-B’ [click to enlarge]

On the 1800 UTC Air Mass RGB image, a northwest-to-southeast oriented cross section line (Baseline B-B’) was positioned through the area of highest PV1.5 pressure values (above). The Baseline B-B’ cross section of model wind speed, potential vorticity and specific humidity (below) displayed a tropopause fold, as the dry air and high potential vorticity characteristic of stratospheric air descended southeastward around the upper-tropospheric 140-knot jet streak axis.

Cross section of AK-NAM40 model fields along Baseline B-B’, valid at 1800 UTC [click to enlarge]

Categories: GOES-18, NUCAPS, Red-Green-Blue (RGB) images