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.

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

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.

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)

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GOES-17 (GOES-West) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the explosive formation of large pyrocumulonimbus (pyroCb) clouds that were spawned by large wildfires in British Columbia, Canada on 30 June 2021. The 10.35 µm cloud-top infrared brightness temperatures rapidly cooled to the -50 to -60ºC range, easily surpassing the -40ºC pyroCb threshold — and pyroCb 3.9 µm cloud-top infrared brightness temperatures were warmer (darker shades of gray) than those of surrounding meteorological cumulonimbus clouds (due to the presence of smaller ice crystals and smoke particles, which were better reflectors of incoming solar radiation).

GOES-17 Fire Temperature RGB images (below) include surface reports plotted in yellow — note that the temperature reached 115ºF (46.1ºC) at Kamloops (CYKA), just southeast of the largest fire. In addition, farther to the southwest, surface observations at Lytton (CWLY) ceased as of 01 UTC (6 PM local time), as another wildfire began to destroy 90% of that town.

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On a smaller spatial and temporal scale, GOES-17 Visible, Shortwave Infrared and Infrared Window images (above) revealed the brief formation of a pyroCb that was produced by the Lava Fire in far northern California. A portion of the cloud top reached the -40ºC threshold (darker shades of blue) to qualify as a pyroCb.

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GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the circulation of Subtropical Storm Raoni (discussion issued by MARINHA) off the coast of Argentina/Uruguay on 28 June 2021.

In the corresponding GOES-16 “Clean” Infrared Window (10.35 µm) images (below), the coldest cloud tops exhibited infrared brightness temperatures around -50ºC (shades of yellow).

===== 29 June Update =====

GOES-16 Visible images (above) showed that Subtropical storm Raoni continued its northeastward motion, and was located off the coast of far southeastern Brazil on 29 June (12 UTC surface analysis | discussion).

GOES-16 Infrared images (below) indicated that Raoni was unable to maintain a persistent closed ring of cold clouds around its center.

A sequence of ASCAT surface scatterometer winds (source) from Metop-A and Metop-C (below) revealed swaths of wind speeds of 40 knots or greater within the northeastern and southwestern sectors of the system.

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Update: Tropical Depression 4 strengthened to become Tropical Storm Danny at 1905 UTC on 28 June (link).

GOES-16 visible imagery (0.64 µm), above, from the morning of 28 June 2021, shows a compact low-level circulation east of South Carolina, steadily moving towards the coast. Deep convection with this system is offset to the east, suggestive of shear, and the shear analysis from the SSEC Tropical website, below, does show easterly shear over the system.

VIIRS Day Night Band imagery, below, from Suomi-NPP at 0723 UTC on 28 June, a time with ample lunar illumination, shows convection over the center of the storm at that time.

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The wind shear analysis from 1900 UTC, below, is more in line with what might be expected in a system with an exposed low-level circulation center.

 

The National Hurricane Center initiated statements on this tropical system at 1500 UTC on 28 June 2021. Refer to those webpages (link) for further information. Tropical Storm warnings are in effect for parts of the South Carolina coast, from Edisto Beach to the S. Santee River.

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