Using Polar-Orbiting Satellite Imagery from Direct Broadcast sites to understand Elsa

July 6th, 2021 |

Suomi NPP Adapative Day Night Band imagery, 0636 UTC on 6 July 2021 (Click to enlarge)

AOML (The Atlantic Oceanographic and Meteorological Laboratory) maintains a Direct Broadcast antenna site that holds satellite imagery (created using CSPP — the Community Satellite Processing Package) created when a tropical system — such as Elsa — is within the download footprint of the AOML antenna.  This imagery — particularly in the microwave — is useful to describe the system’s structure. The Day Night Band image above, from Suomi NPP at 0636 UTC, shows a non-symmetric storm with the bulk of clouds to the east and south of the surface center (at that time near 23.9 N, 82.3 W, i.e., in the Florida Straits to the south of Dry Tortuga).  Rainfall, as diagnosed using MIRS algorithms and microwave ATMS (Advanced Technology Microwave Sounder) data from NPP, below, shows the asymmetry of the storm as well:  almost all the diagnosed rain is east of the center. (It’s helpful that both infrared imagers and microwave sounders are on the same satellite!)

Suomi NPP ATMS-derived Rain Rate, 0637 UTC on 6 July 2021 (Click to enlarge)

The GCOM-W1 (supported by JAXA) satellite also scanned Elsa shortly before 0700 UTC on 6 July.  Microwave observations at ~36 GHz, below, and at 89 GHz, farther below, can help to characterize the structure of the storm. Indeed, observations at/around 85-89 GHz are used in the MIMIC TC product as described here.

GCOM AMSR-2 observations at 36.5 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

GCOM AMSR-2 observations at 89.0 GHz, 0649 UTC on 6 July 2021 (Click to enlarge)

In addition to the AOML site, the CIMSS Direct Broadcast site contains Polar Orbiting imagery in near-real time. The afternoon 88.2 GHz image from (NOAA-20) ATMS is shown below.  Cold cloud tops associated with strong scattering by ice of the 88.2 GHz signal are apparent.

NOAA-20 ATMS Channel 16 Brightness Temperature, 1845 UTC on 6 July 2021 (Click to enlarge)


There are a multitude of polar orbiters such that observations show up in clusters of time.  However, for a better time animation, it’s still best to rely on GOES-16!  The animation below, from CSPP Geosphere, shows a sheared storm south and west of Ft Myers FL.  Indeed, an 1800 UTC 6 July 2021 shear analysis from the CIMSS Tropical website (here, from this site), shows westerly shear of 25-30 knots.

GOES-16 True-Color imagery, 6 July 2021 from 1730 to 1920 UTC (Click to animate)

For the latest information on Elsa, consult the webpages of the National Hurricane Center, or the SSEC/CIMSS Tropical Weather Page.

Convective nowcasting over Wisconsin with NUCAPS

July 5th, 2021 |

Day Cloud Phase Distinction RGB, 1751 UTC on 5 July 2021 (Click to enlarge)

GOES-16 Day Cloud Phase Distinction at 1751 UTC, above, shows two cumulus fields over Wisconsin:    a linear cloud field oriented west-southwest-to-east-northeast over the southern part of the state, and a larger field of agitated cumulus over the northern half of the state, with isolated glaciated storms near the border of Wisconsin and the Upper Peninsula of Michigan.  Would you expect those cumulus fields to develop during the course of afternoon heating?  SPC had much of Wisconsin in a Marginal Risk of severe weather at 2000 UTC on 5 July (link; 1630 and 1300 UTC outlooks were the same), as shown below.

SPC Convective outlook, 2000 UTC on 5 July 2021 (Click to enlarge)


GOES-16 Day Cloud Phase Distinction RGB along with Sounding Availability points from NOAA-20 NUCAPS, 1849 UTC on 5 July 2021 (Click to enlarge)

A benefit of NUCAPS (NOAA-Unique Combined Atmospheric Processing System) profiles (click here for previous blog posts discussing NUCAPS) from NOAA-20 over the contiguous United States (CONUS) is timing: profiles occur between 1600 UTC on the east coast and 2100 UTC on the west coast and thereby sample the atmosphere before the development of diurnal convection. Such was the case over Wisconsin on 5 July 2021. The image above shows the GOES-16 Day Cloud Phase Distinction and the Sounding Availability points from NUCAPS (NOAA-20) at 1849 UTC. The NUCAPS profiles allow a forecaster an independent (independent of models such as NAM or HRRR; see for example, this screen-capture of a 6-h forecast of radar reflectivity from the 1800 UTC/5 July HRRR of convection showing some development over southern WI) estimate of atmospheric stability. How does this diagnosed stability agree with (or not) model forecasts?

700-900 mb NUCAPS relative humidity fields, below, show a drier atmosphere of over southern Wisconsin than over the northern half of the state. (NWS ITOs note: there are instructions in VLab to modify NUCAPS gridding so that the pieces shown in AWIPS are more contiguous than in this blogpost example!).  Lapse rates (also 700-900 mb), below, show weaker stability over northern Wisconsin.  The combination of weaker stability and more moisture might push a forecaster to diminish convective concerns over parts of southern Wisconsin, and maintain those concerns over the northern half of the state. (GOES-16 Total Precipitable Water fields at 1851 UTC — link — show two axes of moisture over Wisconsin: one with the southern area of cumulus development, and one over central Wisconsin)

NUCAPS-derived estimates of 900-700 mb relative humidity, 1901-1912 UTC on 5 July 2021 (Click to enlarge)

NUCAPS-derived estimates of 900-700 mb Lapse Rates 1901-1912 UTC on 5 July 2021 (Click to enlarge)


Convection did not occur with the southern line of cumulus. See the animation below.

GOES-16 Day Cloud Phase Distinction RGB, 1751 UTC 5 July – 0031 UTC 6 July 2021 (click to enlarge)

Hurricane Elsa

July 2nd, 2021 |

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

Elsa was upgraded to a Category 1 hurricane at 1230 UTC on 02 July 2021 — and 1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the tropical cyclone during and after the time period that it began to spread hurricane-force winds across the islands of Barbados and St. Lucia. Pulsing overshooting tops exhibited infrared brightness temperatures in the -80 to -87ºC range (shades of purple).

GOES-16 Infrared images with an overlay of deep-layer wind shear from the CIMSS Tropical Cyclones site (below) indicated that Elsa was moving through an environment of low shear.

GOES-16 Infrared images, with an overlay of deep-layer wind shear at 20 UTC [click to enlarge]

GOES-16 Infrared images, with an overlay of deep-layer wind shear at 20 UTC [click to enlarge]

Tropical Storm Elsa forms in the Atlantic

July 1st, 2021 |

Night Time Microphysics (at night) and True-Color imagery (during the day) over the eastern Atlantic, 0920 – 1220 UTC on 1 July 2021

Tropical Storm Elsa has formed over the tropical eastern Atlantic Ocean.  True-color imagery from CSPP Geosphere (link) shows the storm with occasional bursts of deep convection.  Elsa has formed at the southern edge of a large area of Saharan Air (shown below, link, from this site), and the storm’s future could be influenced by this dry air.

Saharan Air Layer analysis, 1200 UTC on 1 July 2021 (Click to enlarge)

The abundant dry air to the north of Elsa is also apparent in the low-level water vapor imagery, as shown below.

GOES-16 ABI infrared low-level water vapor (Band 10, 7.34 µm) at 1240 UTC on 1 July 2021. NHC prediction of the 1300 UTC position of Elsa along with 34-knot wind radii are shown (Click to enlarge)

The dry air associated with the SAL shows up nicely in gridded NUCAPS fields, too. The toggle below steps through the CIMSS True Color RGB and GOES-16 Band 10 imagery (7.34 µm) along with 850-700 mb relative humidity from gridded NUCAPS.

CIMSS True Color RGB, GOES-16 ABI Band 10 infrared water vapor (7.34 µm), 850-700 mb relative humidity, 1510 UTC on 1 July 2021 (Click to enlarge)

For more information on Elsa, see the SSEC Tropical Website. Official forecasts are on the website of the National Hurricane Center (link; direct link to Elsa’s webpages there)