1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed Fiona as it intensified to a Category 1 Hurricane just south of Puerto Rico during the morning hours on 18 September 2022. The coldest cloud-top 10.35 µm infrared brightness temperatures were around -88ºC.

The corresponding 1-minute GOES-16 Cloud Top Temperature and Cloud Top Height derived products are shown below — the coldest Cloud Top Temperature values were around -91ºC, while maximum Cloud Top Height values were around 61,000 feet.

The highest wind gust at Buoy 42085 — located just south of Ponce (station identifier TJPS) — was 72 knots (83 mph) at 16 UTC (below).

Although Fiona was moving across relatively warm water, GOES-16 Infrared Window (11.2 µm) images with contours of deep-layer wind shear from the CIMSS Tropical Cyclones site (below) indicated that the storm was moving through an environment of moderate shear.

Hurricane Fiona later made landfall in far southwestern Puerto Rico around 1920 UTC — a DMSP-18 image at 2013 UTC (below) showed the eye as it was beginning to move into the Mona Passage.

A prolonged period of strong winds and heavy rainfall from Fiona led to widespread power outages and flash flooding across much of Puerto Rico.

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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 affecting western Alaska today had easily the lowest MSLP (1950-present) for September in the northern Bering Sea, and based on ECMWF analyses it even beat winter/all-time records along part of its track. (To be confirmed when ERA5 data is in) @AlaskaWx @NWSFairbanks pic.twitter.com/2Nq859HxIy

— World Climate Service (@WorldClimateSvc) September 18, 2022

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.

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).

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

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.

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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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