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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Southern Wisconsin experienced the convergence of 3 cooling mechanisms during the afternoon hours of 16 May 2023: (1) the arrival of a dense band of smoke aloft — transported southward from wildfires in Alberta and Saskatchewan — which reduced incoming solar radiation, (2) a southward-moving cold front and (3) the inland surge of a lake breeze (or “Pneumonia Front“) from Lake Michigan. Signatures of all 3 features were evident in GOES-16 (GOES-East) True Color RGB images from the CSPP GeoSphere site (above), with the cold front and lake breeze marked by broken lines of cumulus clouds that could be seen through the thick veil of smoke.

In a comparison of GOES-16 Day Land Cloud RGB images at 1826 UTC that include readouts of Aerosol Optical Depth (AOD), MVFR Fog Probability, Land Surface Temperature and Fire Temperature derived products for a point beneath the thick smoke layer (above) and just south of the thick smoke layer (below), the degree to which the smoke was reducing the amount of incoming solar radiation was apparent in a reduction in Land Surface Temperature (78.26ºF beneath the thick smoke where the AOD was 2.08, vs. 83.98ºF just south of the thick smoke where the AOD was negligible). Both points — and the W-E oriented band of thickest smoke — were located south of the approaching cold front (1800 UTC surface analysis).

CIMSS Natural Color RGB images (below) include plots of surface and buoy reports along with frontal analyses — note the significant drop in air temperatures across southeast Wisconsin as the lake breeze moved inland (for example, from the low 80s F to the middle 50s F within a 30-45 minute period at Milwaukee and Racine; further inland, a notable temperature drop was also seen in Madison just after 19:30 or 7:30 PM local time). Water temperatures reported by Buoy 45007 in southern Lake Michigan were in the 44-46ºF range during the day, and just after 1800 UTC the NOAA-20 VIIRS Sea Surface Temperature value over that buoy location was 47ºF.

A plot of lidar backscatter (source) at Madison, Wisconsin (below) depicted increasing smoke within 2 layers: one at an altitude around 3 km, and another within the 5-6 km altitude range.

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