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.

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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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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).

 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.

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

https://twitter.com/AlaskaWx/status/1569724243864334336

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A CSPP Geosphere mp4 animation from late on 10 September, above (link), shows the development of a pyrocumulus cloud at the south edge of the Cedar Creek fire complex in Oregon (previously discussed here, here and here). The animation above starts at 2101 UTC, shortly after a NOAA-20 overpass above the region. NUCAPS profiles over the regions can define the thermodynamics to help forecasters determine is pyrocumulus clouds might develop. The Green points in the sounding availability plots, below, denote retrievals that converged to a solution using both microwave and infrared data from the ATMS and CrIS instruments, respectively. This includes the profiles near the very warm Cedar Creek fire pixels in east-central Oregon. (Here is a zoomed-in view over the fire with GOES-17 FDCA Fire Power observations; note the two different regions of active fire).

The animation below steps through 3 NUCAPS profiles near the fire. A dry atmosphere is apparent, but note also the very steep lapse rates. If convection develops, aided by the heat of the fire, there is little to inhibit its growth to the tropopause.

NUCAPS profiles can be gridded to provide horizontal fields of thermodynamic variables. The lapse rate computed from 850 and 500 mb temperatures, below, also shows very steep lapse rates (note that portions of Oregon are at/above 850 mb and no data are available).

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One things that happens when a Pyrocumulus develops: the cloud is trackable (in contrast to any surrounding smoke). The CSPP Geosphere animation below (link) shows the Night Microphysics (at night) and True-Color (during the day) — the cloud can be tracked until is dissipates near dawn, and the true-color imagery the next day shows the smoke associated with the pyrocumulus has also moved to the east. Note also in the animation how the active fires show up in the GOES-17 Night Microphysics as different shades of magenta.

Although infrared imagery is challenged to view smoke at night, as suggested in the animation above, the VIIRS Day Night band sees it (if there is sufficient illumination by the Moon). That was the case early on 11 September, as shown below (in an image taken from the VIIRS Today website). Both the light signature from fires are apparent as is the smoke plume from the pyrocumulus.

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AWIPS Satellite imagery in this blog post were created using the TOWR-S AWIPS. Thank you!

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