Tropical Storm Laura’s path near/over the Greater Antilles has affected her strength, and the relative lack of organization means that night-time satellite identification of the center is a challenge. Consider the animation above. Northerly shear (analysis from this site) has shifted the coldest cloud tops to the south of the circulation center and with the 5-minute routine CONUS imagery, it is difficult to discern a surface circulation along the south coast of Cuba, where it was moving.  (A cluster of convection does appear there, although it is initially dwarfed in size by the convection to the south, south of 20 Latitude)

Visible imagery that becomes available at sunrise does show the center. The center gains prominence in the infrared as well as the convection to the south weakens. Note that the center can be discerned within the 1-minute shortwave infrared (3.9 µm) imagery from GOES-16 Mesoscale Sector 1: this link shows data from 0702 to 0803 UTC.  In the greyscale enhancement used in the linked-to animation, coldest cloud tops appear black and speckled because of a lack of precision at very cold temperatures in the 3.9 µm channel).

Sometimes, Day Night Band imagery from VIIRS can be useful in identifying tropical cyclone centers at night (see these 2016 examples with Matthew and Karl, for example). On the morning of 24 August, however, reflected moonlight was nil (Moonset over Cuba today was around 0500 UTC); in addition, the NOAA-20 overpass had Laura near the edge of the scan. Adaptive DNB imagery from Suomi NPP (just after 0700 UTC) and NOAA-20 (just before 0800 UTC), from the Direct Broadcast site at AOML in Miami, do show low clouds just south of Cuba, near the Jardines de la Reina, but it is a challenge to identify a surface circulation from this DNB imagery.

Interests in Cuba and along the Gulf Coast of the United States should monitor closely the progress of Laura. Refer to the National Hurricane Center website for the latest forecasts.

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Tropical system Marco (formerly a category 1 Hurricane) was weakened by shear overnight and early morning on 24 August (as forecast).  The half-hourly animation above, of GOES-16 Band 10, i.e., infrared “low-level” water vapor (7.3 µm), overlain with derived motion winds at upper (red) and lower (blue) levels (Click here to see only the water vapor animation;  here is the shear analysis from the SSEC Tropical website; Note in the animation how the number of low-level vectors increases greatly at the end of the animation as visible imagery becomes available at sunrise.  Also:  the shear in the eastern part of the domain, over the Florida Straits, suggests a favorable environment for Tropical Cyclone Laura, approaching western Cuba from the east) shows the effect of shearing.

Low level easterlies and upper-level southwesterlies mean that the vertical structure of the storm was interrupted:  the low-level circulation decoupled from the upper-level.   That is, the low-level circulation moved to the west as the mid- and upper-level parts of the storm moved north and east.  Result:  By sunrise, visible imagery (0.64 µm) showed the low-level swirl of the elongating near-surface circulation southeast of the mouth of the Mississippi River, and south and west of the main convection over and offshore of the northwest Florida panhandle.

For more information on Tropical Storm Marco, refer to the pages of the National Hurricane Center.

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1-minute Mesoscale Domain Sector 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 formation of a pyrocumulonimbus (pyroCb) cloud that was spawned by the Castle Fire in California on 23 August 2020.

The coldest pyroCb cloud-top infrared brightness temperatures were around -50ºC –according to 00 UTC rawinsonde data from Las Vegas, Nevada (below) indicated that this temperature corresponded to altitudes around 12 km.

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1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images — with and without an overlay of GLM Flash Extent Density (above) showed Marco as it intensified from a Tropical Storm to a Category 1 hurricane at 1630 UTC on 23 August 2020. A pronounced semi-circular convective burst was seen to develop near the storm center shortly before 19 UTC.

A toggle between time-matched Infrared images from Suomi NPP and GOES-16 (below) indicated that the coldest cloud-top infrared brightness temperature on the Suomi NP VIIRS image was -86.8ºC, compared to -81.5ºC from the GOES-16 ABI instrument (the same color enhancement has been applied to both images). The northward parallax displacement associated with GOES-16 imagery over the southern Gulf of Mexico was also apparent.

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