GOES-17 Air Mass RGB images, with hourly plots of surface reports [click to play animated GIF | MP4]

GOES-17 (GOES-West) Air Mass RGB images with hourly plots of surface reports (above) showed the remnants of ex-Typhoon Merbok (storm track) moving northward across the Bering Sea (surface analyses) on 16 September 2022. This strong extratropical cyclone had an anomalously-low surface pressure as it moved northward — in fact, its central Mean Sea Level Pressure set a record for the month of September in the Bering Sea:

The storm center passed just northwest of Buoy 46035, where the peak wind gust was 68 knots (78 mph) at 1800 UTC and 1900 UTC on 16 September. These strong winds caused wave heights to 52 feet, which resulted in a notable upwelling of cooler water. Such strong southwesterly surface winds in the vicinity of Buoy 46035 occurred beneath a swath of anomalously-strong 925 hPa winds within the southeast quadrant of the storm. Two particularly adverse impacts of these strong winds were coastal erosion and flooding across much of western Alaska (more of the storm’s impacts are discussed here).

In the Air Mass RGB images, deeper shades of red-to-orange in the vicinity of the storm center vhighlighted areas where there was enhanced ozone within the atmospheric column (due to an anomalously-low tropopause ) — overlays of AK-NAM40 model Potential Vorticity (PV) 1.5 pressure (below) indicated that the “dynamic tropopause” near the storm center may have descended as low as the 900 Pa pressure level.

GOES-17 Air Mass RGB images, with overlays of AK-NAM40 model PV1.5 pressure [click to play animated GIF | MP4]

In a larger-scale view of GOES-17 Air Mass RGB images created using Geo2Grid (below), one interesting feature was a distinct plume of moist tropical air (highlighted by darker shades of green) that moved northward across the Aleutian Islands into the Bering Sea (for example, at 0600 UTC on 16 September in the warm sector of the storm).

GOES-17 Air Mass RGB images [click to play animated GIF | MP4]

The MIMIC Total Precipitable Water product (below) showed the north-northeastward transport of tropical moisture as Typhoon Merbok transitioned to an extratropical storm.

MIMIC Total Precipitable Water product [click to play animated GIF | MP4]

Additional information pertaining to this event is available here. 

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Typhoon Merbok became a very strong extratropical storm as it moved through the Bering Sea on 15 – 16 September. The animation above shows the development (in the eastern third of the domain) of the tropical cyclone and, starting later in the day on 14 September, its subsequent interaction and merger with a mid-latitude system that moves out over the Pacific Ocean from Asia. The deep red/orange region in the Himawari-8 airmass RGB is associated with strong descent in association with an intrusion of stratospheric air with higher potential vorticity. The potential vorticity structure of this system is discussed in more detail by Prof. Jon Martin (UW Department of Atmospheric and Oceanic Sciences) here at that Department’s weekly Weather Watch (starting at 44 minutes).

Himawari-8 data in this animation is courtesy JMA. Note in the animation the persistence of Typhoon Nanmadol. That typhoon has generated significant swell and the National Weather Service in Guam issued High Surf Advisories from Guam to Saipan. Also, the daily appearance of Keep-Out Zones (see a previous blog post on this subject; here is a NESDIS/OSPO site on the topic) is apparent on the western and eastern limbs of the globe.

Back in 2014, Typhoon Nuri also evolved into a very strong Bering Sea extratropical cyclone — albeit much later in the year! (Link)

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At the request of the National Weather Service forecast office in Guam (where the National Weather Service’s day begins), CIMSS is computing a small region of LightningCast Probabilities that uses Himawari-8 data. The Guam forecast office issues a lightning ‘advisory’ if lightning is possible or occurring within 20 mi of the Guam Airport, and a lightning ‘warning’ if lightning is possible/occurring within 5 mi of the airport. LightningCast probabilities will help in this task. Forecasters will be evaluating its performance in the coming weeks.

LightningCast imagery is available in a RealEarth instance here (at that website, there is a small drop-down menu titled ‘Select Sector’; Choose Guam). An example animation is shown above. (Guam is located at the outer fringes of Typhoon Nanmadol in the image) In contrast to the scenes under GOES-East’s and GOES-West’s view, GLM data are not available. In the forecast office, ground-based lightning sources are available. This animation (from John Cintineo, CIMSS) shows LightningCast probabilities with Earth Networks Total Lightning. Animations online, as shown above, show only Himawari-8 data and LightningCast probability contours.

As with GOES-R LightningCast computations, Himawari-8 uses Visible (0.64 µm), near-infrared (1.61 µm) and infrared (10.41 µm and 12.3 µm) observations. Resolution differences at 1.61 µm (1 km for GOES-R and 2 km for Himawari-8) and slight differences in infrared spectral responses, especially for band 13 (centered near 10.33 µm for GOES-R and 10.41 µm for Himawari-8) may have an as-yet unknown impact on LightningCast probabilities.

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Suomi-NPP VIIRS Visible images [click to play animated GIF | MP4]

A sequence of Suomi-NPP VIIRS Visible images (above) showed a large area of ice-free water in the western Beaufort Sea and eastern Chukchi Sea north of Alaska — with limited sea ice concentration as far north as 80º N latitude — on 13 September 2022.  

False Color RGB images from NOAA-20 and Suomi-NPP, viewed using RealEarth (below) provided another depiction of the large ice-free region the Beaufort Sea (as well as adjacent portions of the Chukchi Sea).

False Color RGB images from NOAA-20 and Suomi-NPP [click to play animated GIF]

 Sea Ice Concentration (based on the NOAA Enterprise Algorithm) at 0000 UTC on 13 September (below) also showed limited ice coverage and concentration extending past 80º N latitude.

Sea Ice Concentration at 0000 UTC on 13 September [click to enlarge]

According to Rick Thoman (University of Alaska, Fairbanks), Beaufort Sea ice extent was the 9th lowest on record for this date:

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