The potent cyclone (surface analysis, an airmass RGB animation from the College of Dupage website is below) that caused severe weather over Hawaii (blog post) is also drenching the islands with considerable rains. The animation of MIMIC Total Precipitable Water, above, shows the storm drawing tropical moisture northward from the Intertropical Convergence Zone. The airmass RGB, below, also shows that connection to the tropics, with the green area in the RGB that is moving northward over Hawaii.

How have various estimates of precipitation quantified the rains that have fallen? Hourly CMORPH-2 Rain Estimates captured at this RealEarth site (enter ‘CMORPH’ into the Search box; this website has data through 31 December 2024), below, capture the progress of the heavy rain band across the islands, mostly west to east, but with a couple of seemingly backward steps.

In contrast, GOES-18 GREMLIN estimates of MRMS radar reflectivity, shown below with GOES-18 mid-level water vapor infrared imagery, shows steady eastward progress to the heavy rainband. A band of lighter precipitation persists over Kauai however. The animation below suggests the backward steps in the CMORPH hourly precipitation shown above are artifacts that bear investigation. A discussion on how GREMLIN rain estimates are used over Pago Pago in the south Pacific is available here.

There is a direct broadcast antenna at Honolulu Community College (link) and microwave data from that site can be used to derive instantaneous rain rates (via MIRS algorithms). The animation below shows three snapshots between 0715 and 1215 UTC.

How do the instantaneous rain rates compare with GREMLIN MRMS estimates? Three comparisons are shown below. The figures are qualitatively similar.

When evaluating heavy rains, there are many products available to a forecaster. Use them all to increase confidence in the diagnostics.

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With the increasing threat for strong to severe convection across the western portion of Hawai’i, a Severe Thunderstorm Watch was issued for an area centered on the island of Kauai at 1522 UTC on 30th January 2025 (above).

5-minute CONUS Sector GOES-18 Clean Infrared Window (10.3 µm) images (above) showed elongated clusters of convection moving eastward and northeastward across Kauai and Oahu — with embedded thunderstorms that produced heavy rain and strong winds on those two islands (Local Storm Reports).

A corresponding animation of GOES-18 Infrared images with an overlay of GLM Flash Extent Density (below) displayed the abundant lightning activity associated with these thunderstorms.

This convection was occurring within the warm sector of a deepening Gale Force to Storm Force low pressure system (bottom left on these surface analyses) that was located NW of the island chain — and the strong SW flow in advance of this storm system (and its cold front) interacting with island terrain produced wind gusts as high as 120 mph on Maui at 0850 UTC.

The air mass within the warm sector was also unusually moist — in fact, a new daily record rainfall of 3.57 inches occurred at Honolulu. The Total Precipitable Water (PW) value of 1.98″ derived from Lihue, Kauai rawinsonde data at 1200 UTC on 30th January was a record high value for that date/time, according to the SPC Sounding Climatology site (below).

The PW value derived from Lihue rawinsonde data at 1800 UTC on 30th January (about 2.5 hours after the Severe Thunderstorm Watch was issued) was even higher, at 2.06″ (below).

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Geo2grid software accesses SatPy libraries that allow for the reading of level-1c netcdf files holding FCI (Flexible Combined Imager) data from the latest operational Meteosat satellite (Meteosat-12). So if you can access to that output, you can create beautiful images as the ones shown above. The RGB shows a storm moving into western Europe. The Red/Orange in the image is associated with the Potential Vorticity Anomaly helping to support the storm (a second Potential Vorticity Anomaly is apparent over the central Mediterranean, and there seems to be one over the Arabian Peninsula too — maybe that’s a Westerly Disturbance for India later this weekend) To create the image above, I first moved all 40 (!) image sectors holding the data valid at 0000 UTC on 30 January 2025 to my computer that holds the geo2grid software (downloadable from this link). The geo2grid documentation includes a section on readers, including the FCI Level-1c reader.

The two geo2grid commands to create the image above are shown below. One creates the .tif file, one adds coastlines to the image. In geo2grid call, those last 4 wildcards (????) refer to the 40 different sectors (that is, 0001, 0002, 0003, 0004, … , 0039, 0040) that hold the data. The 0001 in the filename refers to the 1st image of the day.

./geo2grid.sh -r fci_l1c_nc -w geotiff -p airmass -f /pathtoL1CData/W*FDHSI*_0001_????.nc
./add_coastlines.sh --add-coastlines --coastlines-resolution f MTG-I1_FCI_airmass_20250130_000000_mtg_fci_fdss_2km.tif 

As with other geo2grid commands, one can create a region into which you can subsect the data so you can focus on a particular region. This was done below to focus on parts of Europe.

/p2g_grid_helper.sh Europe4 10.0 45.0 4000 -4000 1440 1120 > Europe4.yaml
./geo2grid.sh -r fci_l1c_nc -w geotiff -p airmass -g Europe4 --grid-configs ./Europe4.yaml -f /pathtoL1CData/W*FDHSI*_0001_????.nc 
 ./add_coastlines.sh --add-coastlines --coastlines-resolution f MTG-I1_FCI_airmass_20250130_000000_Europe4.tif 

The output from that series of calls is shown below.

Thanks to EUMETSAT for sharing the data that allowed the creation of these beautiful images!

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Red Visible (0.64 µm) images (above) showed a long, narrow convective cloud band associated with a strong cold front that was moving southward and southeastward across New York and Pennsylvania on 29th January 2025. Strong winds coupled with moderate-to-heavy snow along this cloud band prompted the issuance of numerous Snow Squall Warnings across the area. The appearance of intermittent GLM Flash Extent Density and GLM Flash Point signatures suggested that thundersnow may have occurred with some of these snow squalls. Note the slight northward displacement of the Flash Extent Density pixels compared to the Flash Points (1659 UTC image) — this is because the commonly-used Gridded GLM products (such as Flash Extent Density, Minimum Flash Area and Total Optical Energy) are not corrected for parallax, as the GLM Flash Points are.

5-minute CONUS Sector GOES-19 (Preliminary/Non-operational) Day Cloud Phase Distinction RGB images created using Geo2Grid (below) helped to highlight this cold frontal cloud band — the shades of green to yellow indicated that the cloud band was either mixed phase or fully glaciated.

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