The system that produced the high-impact flooding event on Maui (discussed here) also  caused flooding rains on Oahu on the 9th.   (A Flash Flood Emergency was declared at 348 HST on 9 March:  Link)  How well did quantitative satellite estimates of this event perform?  Hydroestimator values, above, from the 24 hours ending 1200 UTC on 9 March (from this website) show isolated maxima over northern Oahu for and over eastern Maui. Daily totals for the 24 hours ending 1200 UTC on 10 March are shown below.  Again, heavy rain is diagnosed on Maui with lesser amounts over Oahu, where 48-hour  totals  were between  150  and  200  mm.

24-hour totals from JAXA’s GsMAP website, above, show large values mostly north of Oahu, and also just north of Maui.  Values are between 100-150 mm.  24-hour CMORPH-2 values (from RealEarth), below, ending 0000 UTC on 10 March, show values between 50 and 100 mm.  Values over Maui are less than 50 mm.

The GOES-17 Enterprise algorithm totals, below (courtesy Bob Kuligowski, NOAA) , show values close to 50 mm over Oahu, and over 50 mm on Maui.

None of these rain totals captured the exceptional nature (writeup is here;  some totals are here) of this orographically enhanced rainfall. The widespread nature of the rain was captured however.  All methods detected heaviest rain north of the Island chain.

GOES-17 animations, both visible and infrared, combined with situational awareness driven by animations of total precipitable water, such as that below (from this site) will help a forecaster anticipate heavy rains however — when they might start, and when they might end.

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GOES-17 (GOES-West) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) revealed 2 bursts of back-building thunderstorms that produced heavy rainfall (as much as 19.21 inches) and flooding along the northern coast of the Hawaiian island of Maui on 08 March 2021. This heavy rain caused rockslides that closed some roads, and prompted evacuations of a few communities downstream of the Kaupakulua Dam (which began to experience over-topping).

The coldest 10.35 µm infrared brightness temperatures were around -48ºC — for example, at 0000 UTC on 09 March (below).

In closer views of GOES-17 Visible and Infrared images (above), USGS river and rain gauge locations are plotted in large yellow text — the abrupt rise in flow of the Honopau Stream near Huelo (HPOH1) and the rapid accumulation of 17 inches of rainfall at the Wailuaiki rain gauge near Keanae (WWKH1) are shown below.

GOES-17 Water Vapor images with plots of mid-upper level Derived Motion Winds (above) showed the circulation of an upper level low west of the Hawaiian Islands — and with an increase in southwesterly upper-tropospheric wind speeds (as shown in Lihue rawinsonde data). the corresponding upper-level divergence (below) was seen to increase across the island chain by 00 UTC on 09 March (providing a more favorable environment for the development of deep convection).

The MIMIC Total Precipitable Water product spanning the 2 day period leading up to the heavy rainfall (below) showed an axis of higher tropical moisture — with TPW values of 1.50 to 1.75 inches — moving westward across Hawai’i.

The TPW value calculated from Hilo, Hawai’i rawinsonde data increased from 37.8 mm to 42.3 mm (1.49 inches to 1.67 inches) during the day as the lobe of enhanced moisture began to move westward over the Big Island (below).

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and Shortwave Infrared (3.9 µm) images (above) depicted smoke plumes and thermal anomalies (clusters of hot pixels) associated with widespread prescribed burns across parts of Oklahoma, Arkansas and Missouri on 07 March 2021.

For one of the largest fires in far southern Oklahoma (located about 15 miles north-northwest of Ardmore), a 4-panel comparison of 5-minute GOES-16 Shortwave Infrared images with components of the Fire/Hot Spot Characterization algorithm — Fire Temperature, Fire Power and Fire Area — is shown below. The highest 3.9 µm infrared brightness temperature (114.8ºC or 387.95 K) and Fire Power (1555 MW) values were seen at 2036 UTC, while the highest Fire Temperature value (924.5 K) occurred at 2056 UTC.

With a broad ridge of high pressure centered over the Lower Mississippi River Valley (surface analyses), its anticyclonic flow could be seen via smoke plumes from multiple prescribed burns across the Deep South — as highlighted by GOES-16 True Color RGB images created using Geo2Grid (below).

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Accumulating hail fell in Daytona Beach FL (Link) on 6 March 2021 in association with a front over the Florida peninsula.  Preliminary storm reports from SPC (link) show reports of 1″ to 1.75″ hail. (The region was under a general thunderstorm outlook from SPC: link). The animation above shows the Convection RGB from 1431 through 1701 UTC on 6 March, bracketing the hail event over Daytona Beach near 1600 UTC. A strong white/yellow signal develops in a cell over Volusia County (Dayton Beach is within Volusia County) around 1545 UTC. This is the cell that deposits the hail.

ProbHail values for this event (from this website) were small, at less than 10%. The value of ProbSevere here could be in identifying the cell responsible for the Hail, and showing values for the radar object that exceed others nearby; that is, providing guidance as to which radar cell to interrogate most often. The image above shows ProbSevere at 1535, just before a Severe Thunderstorm Warning was issued. The image below shows ProbSevere at 1600 UTC, just after the Special Marine Warning was issued (and while the Severe Thunderstorm warning was still in effect).

The time series plot for the radar object that produced the hail is shown below. Note that ProbHail (and lightning) increased (marginally) before the hail events (reported between 1535 and 1615 UTC) before collapsing.

There are several features in the visible imagery, below, that might be affecting the thunderstorm producing the hail. An east-west boundary is moving down the Atlantic coastline, passing through Daytona Beach around 1551 UTC. A very strong reflective signal becomes apparent after 1541 UTC as well (link): the convective cell has penetrated through the cirrus shield in the region.

This was a challenging forecast in a marginal environment.

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