SAR data are being acquired over American Samoa for the next several weeks. SAR data from a Sentinel-1A overpass at 0553 UTC on 31 January, shown above (from this website), shows mostly light winds, mostly less than 10 m/s. The Normalized Radar Cross Section (NRCS) data can be used to view any ice contamination in the wind speed image. Ice can cause very strong reflection of the SAR signal that will be misinterpreted as strong winds. If significant ice is present in any convective tower, it will have a feathery appearance in the NRCS data.

SAR netcdf files can also be imported into AWIPS, and the toggle below compares GOES-18 Band 13 imagery and SAR data at the same time. On this day it is challenging to relate the small increases in wind apparent in the SAR imagery to Band 13 satellite imagery.

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MetopB overflew the Samoan Islands shortly after 0900 UTC (link), and Advanced Scatterometer (ASCAT) winds from that platform also show weak winds. MetopC ASCAT winds from 0831 and 1011 UTC show light winds as well.

Thanks to the NOAA Office of Observations and NOAA/NESDIS/STAR SMCD and SOCD for arranging these observations.

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The Special Collection actually started on 30 January, and two RADARSAT collections occurred, one at 0544 (Wind Analaysis is here; NRCS is here) and one at 1647 UTC (Wind Analysis ; NRCS). Toggles of the two image pairs are shown below.

The 1647 UTC wind speed analysis includes regions where contamination by thick ice in clouds is likely occurring. That is, those very strong wind values (nearly 50 knots!) centered near 16.25 S and 171.5 W are not true surface winds speeds, but arise because of strong reflection from thick ice within convective clouds in that vicinity. (The ice features have a feathery look in the NRCS fields). GOES-18 Band 13 imagery over that region, below, shows abundant deep convection. The GOES-18 Cloud Phase product (here) indicated ice clouds over the convection, but only within certain regions of the convection was the ice thick enough to reflect enough SAR radiation to affect the derived wind speeds.

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GOES-16 (GOES-East) “Red” Visible (0.64 µm) images which include plots of GOES-16 Derived Motion Winds within the Suface-900 hPa layer (above) showed the eastward transport of several ice floes from the northern portion of Green Bay into Lake Michigan on 30 January 2023. Surface wind gusts and Derived Motion Wind speeds were generally in the 15-20 knot range during much of the day.

VIIRS True Color RGB and False Color RGB images from NOAA-20 and Suomi-NPP (below) confirmed that these features were ice floes (snow and ice appear as shades of cyan in the False Color RGB images). The VIIRS data were downloaded and processed by the SSEC/CIMSS Direct Broadcast ground station.

The emergence of ice floes into Lake Michigan can also be seen in a comparison of RADARSAT Synthetic Aperture Radar (SAR) wind data (source) at 1208 UTC and 2332 UTC (below). Ice features are very reflective in SAR wind data, and appear as brighter shades of yellow to red in these 2 images.

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An animation of the Day Cloud Type RGB over Lake Superior on 30 January 2023, above, shows two prominent features: persistent lake-effect bands oriented west-northwest to east-southeast over the western four-fifths of the Lake (station KCMX on the Keewenaw peninsula, for example, observed heavy snow during this animation), and a more north-south oriented convergence band that extends from the eastern Upper Peninsula of Michigan towards Marathon, ON. Note the northeast wind observation on Caribou Island in eastern Lake Superior.

Advanced Scatterometer (ASCAT) winds from Metop-B (that had a timely descending overpass to view Lake Superior), shown below, neatly show the convergent wind field. (Imagery from this website). A 1500 UTC surface analysis (here) shows a trough of low pressure over extreme eastern Lake Superior consistent with the region of northeast winds.

Note that the RGB used above is the Day Cloud Type RGB (rather than the perhaps more well-known Day Cloud Phase Distinction). In very cold airmasses, the ‘red’ band of the Day Cloud Phase Distinction RGB loses the ability to discriminate between the cold ground and higher cloud tops that might have a temperature similar to the Earth’s surface. The Day Cloud Type RGB uses Band 4 (the so-called ‘Cirrus Band’) rather than Band 13. The toggle below compares Day Cloud Type and Day Cloud Phase Distinction RGBs at 1736 UTC. Day Cloud Type is doing a better job on this day in discriminating between the different cloud tops in the Lake-Effect bands and in the convergence band.

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Thanks to Paul Ford, ECCC, for drawing our attention to this interesting convergent band over Lake Superior!

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Auckland, on the North Island of New Zealand, has experienced significant flooding starting on 27 January 2023. MIMIC Total Precipitable Water fields, above, (from this site, or downloadable here) show an atmospheric connection between the deep tropical moisture that is persistent between 5^oS and 20^oS; a filament moves with a cyclonic swirl from 26-28 January. A second region of even more moisture is poised to the north of New Zealand by 0000 UTC 30 January. How unusually wet is this moisture stream? NOAA’s Office of Satellite Products and Observations (OSPO) produces percent-of-normal total precipitable water products, available at this website. The values near New Zealand early on 27 January are around 150% of normal, as shown below.

Values approaching New Zealand on 30 January 2023, shown below, are somewhat larger: closer to 175% of normal.

Himawairi-9 imagery on 26-27 January 2023, shown below, shows persistent convective development in/around Auckland.

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Rain totals can be estimated from Satellite. GsMap, a website maintained by JAXA, produces hourly and daily rainfall maps, and the 24-hour total ending at 1200 UTC on 27 January (from this link) is shown below. A similar image, but for the 24 hours ending at 1200 UTC on 30 January 2023, also shown below, indicates very large accumulations over the ocean to the north of New Zealand.

CMORPH real-time estimates of 24-hour precipitation are available in RealEarth (enter ‘CMORPH’ in the search box at that website, or click this link for the event discussed in this blog post). Values for the 24 hours ending 2359 UTC on 26 January, and for the 24 hours ending on 27 January, below, show values near 100 mm around Auckland for the two days. Values for the 24 hours ending 29 January show heavy rains moving back on to the North Island.

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GOES-18 also views New Zealand. The animation of the Night Microphysics RGB, below, produced by the CSPP Geosphere site shows the deep clouds (in red) associated with the abundant moisture/tall clouds to the north of New Zealand, with a slow southward motion to the cloud mass.

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