What did the Medicane that hit Greece do afterwards?  VIIRS True-color imagery, above, taken from the NASA WorldView site, show an intact feature moving along the northern coast of Africa on 20-21 September towards the Nile Delta.  The amount of cloudiness is in general declining as it moves into a drier environment.  Total Precipitable Water (TPW) from the MIMIC website shows the general drying surrounding the storm.

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Rick Kohrs, SSEC/CIMSS, supplied the True-Color multi-day animation from Meteosat-11 imagery below. (Updated on 23 September to include date annotations)

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Suomi NPP overflew Tropical Storm Beta off the coast of Texas shortly after 0820 UTC on 21 September (NPP orbits over North America on 21 September are shown below, taken from this site). Day Night band visible imagery shows the swirl of clouds at the center of the storm, off the coast of Texas south of Houston/Galveston and east of Corpus Christi. The 11.45 µm infrared imagery (created using CSPP software and the DB data at CIMSS, and available to NWS offices via an LDM feed) shows the convection that surrounds this center, and also the stronger convection over the Gulf of Mexico to the east.

Both visible and infrared imagery in this case show the storm center. That is not always the case. Sometimes the Day Night band alone identifies the storm center without ambiguity. The Day Night Band at 0813 observed no lightning. The light sources over the open Gulf of Mexico south of Louisiana are drilling platforms.

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The Suomi NPP pass over the eastern Gulf of Mexico, above, from 06 UTC, shows one horizontal streak of brightness in the central Gulf that is a lighting bolt. The Geostationary Lightning Mapper on GOES-16 also observed lightning flashes — how do the two observations compare?

To make that comparison, it’s necessary to determine exactly when Suomi-NPP overflew the eastern Gulf, and that’s suggested in the orbital path figure above. The time stamp for satellite imagery is not the precise time that scanning occurred; historically, the nominal time of an image is the time of the first scan line in the image. For this descending Suomi NPP pass (the satellite is moving from north to south), that time stamp — 0633 UTC — occurred when Suomi NPP was far north of CONUS, north of Quebec.  (Similarly, the time of the 0813 UTC pass shown above has a time stamp when the Satellite was viewing north of Hudson Bay!  During the afternoon, the time stamp for those ascending passes (the satellite is moving from south to north) occurs when the satellite is far south of CONUS). The actual orbit path mapping suggests a scan time over the Gulf Coast at 0643 or 0644 UTC.  Toggles between the Day Night Band image with the lightning streak and the GLM 1-minute observations at 0643 UTC  and at 0644 UTC are shown below.   It appears that the 0644 UTC data better matches the Day Night band imagery, but the comparison is by no means obvious.  This bears further investigation!

 

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Tropical Storm Beta was in the northwest Gulf of Mexico on 20 September 2020. Visible imagery (with GLM overlain) shows two principal regions of convection, one near the center, and one in a long feeder band to the east of the storm. Derived motion winds (this image includes a legend that links vector color to level) show cyclonic low-level motion in the northwest Gulf of Mexico, divergent motion at 500 mb, and strong westerly outflow at 300 mb.

‘Cirrus Channel’ (Band 4, 1.38 µm) near-infrared imagery shows the considerable upper-level cloudiness associated with the central convection and the convective band east of the center. There is also abundant storm outflow to the east and north of the storm.

Visible imagery and low-level winds show cyclonic motion at low levels.  The convection is displaced to the east because of southwesterly shear over the storm (shown below, in an image take from this site).

Both upper-level and low-level water vapor imagery show very dry mid-tropospheric air over Texas. MIMIC Total Precipitable Water, below, (source), also shows the significant dry air over the continent. (Hurricane Teddy is also apparent in the western Atlantic).

Is the dry air influencing the development of this storm? Low-level flow (850-700), below, from this site, shows weak easterly flow. Low-level flow is from regions of deep moisture. Upper-level flow (200-700 mb) shows motion from the (dryer) west. These two different airflows are influencing the development of Beta.

For the latest on Beta, refer to the pages of the National Hurricane Center (direct link for Beta).

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GOES-16 (GOES-East) “Red” Visible (0.64 µm), Shortwave Infrared (3.9 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed a series of pyrocumulonimbus (pyroCb) pulses emanating from the Mullen Fire in southeastern Wyoming on 19 September 2020. Each of the  pulses exhibited 10.35 µm brightness temperatures of -40ºC and colder  (shades of blue) — assuring the heterogeneous nucleation of all supercooled water droplets to form ice crystals, thereby meeting the criteria of a pyroCb.

The coldest cloud-top infrared brightness temperatures were around -47ºC, which corresponded to altitudes near 11 km according to rawinsonde data from Riverton, Wyoming (below).

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