GOES-18 (GOES-West) “Clean” Infrared Window (10.3 µm) images (above) showed the formation of a pyrocumulonimbus (pyroCb) cloud — produced by a wildfire southwest of Fort Nelson, British Columbia (station identifier CYYE) — around 2340 UTC on 19 May 2023. Cloud-top infrared brightness temperatures reached -61ºC as the pyroCb cloud drifted eastward across Alberta.

GOES-18 True Color RGB and Nighttime Microphysics RGB images from the CSPP GeoSphere site (below) showed the late-day pyroCb formation and its subsequent eastward motion after sunset.

VIIRS Infrared Window (11.45 µm) images from Suomi-NPP (valid at 0952 UTC) and NOAA-20 (valid at 1042 UTC) are shown below. Cloud-top infrared brightness temperatures were as cold as -63ºC in the NOAA-20 image (which is mislabeled as NPP).

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Radar imagery over the island of Hawai’i, below, from 512 – 639 AM HST shows the development of strong thunderstorms over/near Kona. Note that 512 AM HST is 1512 UTC; 639 AM HST is 1639 UTC. The heavy rains led to the issuance of a Flash Flood Warning (link). What satellite products might have helped with situational awareness in this event?

MIMIC Total Precipitable Water fields, below, from 0000 UTC on 18 May through 2000 UTC on 19 May, show moisture throughout the Hawai’ian island chain. The total precipitable water at Hilo increased from 40.2 mm to 44.2 mm from 1200 UTC 18 May to 1200 UTC 19 May (link). Sometimes NUCAPS fields from NOAA-20 can give information about the environment in which convection might develop. On 19 May, however, the islands of Maui and Hawai’i sat in between NOAA-20 overpasses, as shown below, using data from this website (Suomi NPP and NOAA-21 sampled the region, but NUCAPS products are not yet operational from NOAA-21, and an anomaly exists in the CrIS instrument on Suomi NPP). This case demonstrates why two JPSS soundings providing operational data are useful. NUCAPS on this day does give an overview of the large-scale thermodynamics: Cold temperatures at 500 mb and (relatively) warm temperatures at 850 mb highlight reduced stability over the Hawai’ian Island chain.

GOES-18 Derived Stability indices — such as Lifted Index, shown below with the default AWIPS enhancement altered so that the range is -5 to 10 — are clear-sky only products. By using animations, however, a user can discern regions where instabilities exist when occasional cloud breaks occur, as shown below. Modest instability (albeit individual pixels!) is diagnosed over the western part of the island of Hawai’i at various times before the outbreak of convection between 1500 and 1600 UTC.

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Different websites show quantitative estimates of precipitation. How did they do for this admittedly small-scale event? CMORPH2 precipitation estimates are available at RealEarth (enter ‘CMORPH’ in the Search box at that website) as shown below, and suggest only 5-10 mm on that day with an apparent minimum over Kona.

GsMap (from JAXA), shown below, does a bit better with the placement of a maximum over Kona. The values — from 20-30 mm — are too light.

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The Joint Typhoon Warning Center has issued a Tropical Cyclone Formation Advisory (TCFA) for disturbed weather located southwest of Chuuk in the tropical Pacific. MIMIC Total Precipitable Water fields, above, show the development of a circulation near 150^oE Longitude and 5^oN Latitude between 0000 UTC 17 May and 0000 UTC 19 May. At present the system is very close to the Equator, and the low latitudes may somewhat inhibit its development in the short term. The circulation of the system is also apparent in Advanced Scatterometry (ASCAT) data from MetopB, shown below and available here. The HY-2C satellite returned scatterometry data over the circulation center, also shown below (taken from this site).

What does the future hold for this system? Dynamic Layer Mean Winds, below, (from the SSEC Tropical Weather website), suggest that in the short term the system might be moving to the northeast (consistent with the track from JTWC here).

The invest is moving over very warm waters, and is in a narrow region of modest shear, as shown in the toggle below.

Himawari9 Clean Window infrared imagery, below, from 00 – 17 UTC on 19 May, shows vigorous convective development just west of 150^oE and south of 10^oN (perhaps some of this intensification in the organization is part of the well-known diurnal cycle in tropical cyclone convection as discussed here, for example). Note also the northward and eastward motion to the north of the convection. There appears to be good ventilation away from the storm (strong upper-level divergence is diagnosed, per this 1500 UTC analysis from the SSEC Tropical Weather website).

The ventilating flow from the storm center is perhaps more apparent in the upper-level water vapor imagery, shown below.

You can find more information on this system at following websites: JTWC. NWS Guam (they recently had a map discussion on Facebook live); SSEC Tropical Website; Tokyo RSMC. The next name for western Pacific tropical systems is Mawar, the Malaysian word for ‘Rose’. Residents of the Guam and other Marianas Islands should pay particular attention to this storm as current forecasts have it moving through that island chain next week.

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Visible imagery from near sunset on 16 May 2023, above, shows multiple horizontal cloud lines north of the islands of Oahu and Kauai. Each of the clouds lines is associated with a local modulation of the wind field in the SAR Wind field. The wind /Normalized Radar Cross Section fields are also available online (winds; NRCS). Note that a SAR Wind scene from this ascending Sentinel-1A pass (here) that was taken just before the one above has an hourglass-shaped feature (at 21.2^oN, 158.4^oW) in the derived wind field that is highlights a mismatch between the first guess field used and the NRCS data.

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