Microwave rain estimates with an MCS

July 29th, 2021 |
VIIRS NPP Day Night Band visible (0.70 µm) imagery from Suomi-NPP (0740 UTC) and NOAA-20 (0831 UTC) on 29 July 2021 (Click to enlarge)

Severe thunderstorms developed (in a moderate risk region from the Storm Prediction Center; here are the Storm Reports) over northern Wisconsin late in the day on 28 July 2021 and moved to the southeast (here is an mp4 animation of GOES-16 imagery courtesy of Tim Schmit, NOAA). The Day Night Band imagery, above, from Suomi NPP (0740 UTC) and NOAA-20 (0831 UTC), shows snapshots of the storms as they moved southward into Illinois. The 0740 UTC image include more evidence of lightning — especially in southwestern Wisconsin (the horizontal streaks of light) and just southwest of Dubuque. At 0831 UTC, lightning is not detected in the Day Night Band image.

In addition to carrying the VIIRS (Visible-Infrared Imaging Radiometer Suite) instrument, Suomi-NPP and NOAA-20 also carry the Advanced Technology Microwave Sounder (ATMS), and microwave data from that instrument can be used to infer rain rates (using MIRS — Microwave Integrated Retrieval System — algorithms, that are part of Community Satellite Processing Package — CSPP — software available to use at Direct Broadcast sites). The toggles show the Day Night Band image, the ATMS-derived Rain Rate (the green region at 0742 UTC is >3″/hour!), and the base reflectivity at 0740 UTC (below) and at 0831 UTC (bottom). The MIRS Rain Rate (0742 UTC; 0833 UTC) product does outline regions where rain is likely falling, and gives credible values where the heaviest rains are falling. Note the diminishing rain rate over southwestern WI, for example, between 0740 and 0830 UTC — indicative of weaker convection — an observation echoed in the changes in lightning detection with the Day Night band. Changes in radar to reflect that difference in microwave-estimated rain rate are a little more subtle.

Because microwave estimates of rain rate are affected by background emissivity, and because water has a much lower microwave emissivity than land, you can sometimes view land/water boundaries (as in the 0742 UTC Rain Rate, below).

MIRS Rain Rate gives useful information about rains when radar observations cannot be accessed.

Suomi NPP Day Night Band visible (0.70 µm) image, ATMS estimates of Rain Rate, and 0.5-degree Reflectivity from a radar composite, all at 0740 UTC on 29 July 2021 (Click to enlarge)
NOAA-20 Day Night Band visible (0.70 µm) image, ATMS estimates of Rain Rate, and 0.5-degree Reflectivity from a radar composite, all at 0830 UTC on 29 July 2021 (Click to enlarge)

MIRS Rain Rate products are available via an LDM feed from CIMSS; they are produced using the Direct Broadcast antenna at CIMSS and are thus very timely.

SAR winds near Tropical Storm Nepartak

July 27th, 2021 |
RCM1 SAR Winds over Tropical Storm Nepartak just east of Honshu, 0828 UTC on 27 July 2021 (Click to enlarge)

RADARSAT Constellation Mission One (RCM1) passed over Nepartak at 0828 UTC on 27 July 2021, and the image above shows the Synthetic Aperture Radar (SAR) winds derived at that time. There is a widespread region of ~40-knot winds (cyan to green in the color enhancement), a bit stronger than the 30-knot winds viewed by MetopA at 1040 UTC (shown here, in this blog post). How certain can a forecaster be of the even-stronger winds that exist in an area near the coast near 37.4ºN, 141.4ºE, and in an arc from 37.5ºN, 142.5ºE to 37.2ºN, 144ºE? There are isolated SAR estimates in that band that are near 60 knots! Are there other data sources to confirm that kind of wind? (See information at the bottom for clarification!)

The image below shows Himawari-8 Clean window imagery at 0829 UTC, just after the image above. Three points with cold cloud tops, suggestive of more vigorous convection, are indicated: (37.6ºN, 141.18ºE); (37.57ºN, 143.01ºE); (37.35ºN, 144.01ºE). The structures in the infrared imagery do match the structures in the SAR winds, but offset a bit to the north in the Himawari-8 imagery, as expected because of the parallax shift: features will be displaced away from the sub-satellite point, with the displacement increasing for higher clouds, and for greater distance from the sub-satellite point (on the Equator at 140.2ºE for Himawari-8). Convective downdrafts could be responsible for the highest winds shown in the SAR analysis.

Himawari-8 Clean Window Infrared (10.41 µm) imagery, 0829 UTC on 27 July 2021 (Click to enlarge)

The strong winds in the image are not observations of strong winds by SAR. Rather, these are most likely the result of reflection off of ice in the atmosphere — ice that is likely to be present around convective towers that have glaciated. (Thanks to Christopher Jackson, GST/NOAA, for this information!)

Tropical Storm Nepartak approaches Japan

July 26th, 2021 |
MIMIC microwave estimates of Total Precipitable Water, 1800 UTC on 26 July 2021 (Click to enlarge)

As the games of the 2021 Olympics progress, a weakening Tropical Storm Nepartak is moving over coastal waters to the east of Honshu, the main island of Japan. The Total Precipitable Water imagery, above, from MIMIC TPW, shows a plume of moisture wrapped around the circulation center. Himawari-8 Clean Window infrared (10.41 µm) imagery, below , from the Himawari-8 Target scene (courtesy of JMA; here’s a link to more JMA satellite imagery), shows the progression of the storm.

Himawari-8 Band 13 Clean Window Infrared (10.41 µm) imagery, 1712 – 2327 UTC, 26 July 2021 (Click to animate)

The forecast from the Joint Typhoon Warning Center (JTWC) as of 1800 UTC has the weakening storm backing into northern Honshu (forecast track; it’s also available from JMA). As of 2300 UTC, the center of Nepartak had moved north to Tokyo’s latitude, and convective bands on the west side of the storm are affecting areas around Tokyo, Yokohama, Sagami Bay and Chiba prefecture. Interests in Japan should monitor closely the progress of this storm.

Visible imagery from shortly after sunrise on Tuesday 27 July in Japan shows the storm to the east of Japan; very little convection is within the storm center.

Himawari-8 Visible Image (0.64 µm), 0024 UTC 27 July 2021

Metop-A overflew Japan at around 1040 UTC on 27 July. Scatterometry (source) showed the wind structure of the storm very nicely.

MetopA Scatterometer winds, 1041 UTC on 27 July 2021 (Click to enlarge)

Tropical disturbance off the US Southeast Coast

July 25th, 2021 |
CSPP GeoSphere animation, 1240-1550 UTC on 25 July 2021

The National Hurricane Center is monitoring an area of disturbed weather over the western Atlantic, to the north of the Bahamas and south of Cape Hatteras. The three-hour animation from the CSPP GeoSphere site (link, above), shows convection and a small low-level cyclonic circulation. This system is drifting to the east, towards Florida, and is in an environment of small values of vertical wind shear (the analysis below is from the CIMSS Tropical Weather Site) that could augur further development. Refer to the pages of the National Hurricane Center for more information.

200-850 Shear Values, 1400 UTC on 25 July 2021. The disturbance center is denoted with an I.

The Day Night Band image from Suomi NPP, below, from the early morning of 25 July 2021, (from the VIIRS Today website) shows the storm under the waning Buck Full Moon. Compare that to the NOAA-20 Day Night Band image from 24 July, the night before (link): the amount of convection decreased between 24 and 25 July.

Suomi NPP Day Night Band imagery, 25 July 2021

On the morning of 26 July 2021, the disturbance is moving into Florida/Georgia. Convection associated with the system is not over its center. (CSPP Geosphere link)

CSPP Geosphere animation, 1320-1610 UTC on 26 July 2021