Tropical Storm Zeta in the Caribbean Sea

October 25th, 2020 |

GOES-16 “Clean” Infrared Window (10.35 µm) images (with and without an overlay of GLM Flash Extent Density) and “Red” Visible (0.64 µm) images [click to play animation | MP4]

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

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Clean” Infrared Window (10.35 µm) and “Red” Visible (0.64 µm) images (above) showed Tropical Storm Zeta in the northwest Caribbean Sea on 25 October 2020. While it remained somewhat disorganized, Zeta slowly intensified from 35 knots to 45 knots during that time period. The coldest cloud-top infrared brightness temperature observed was -94.4ºC.

GOES-16 Infrared images with an overlay of GLM Flash Extent Density (below) did reveal intermittent lightning activity with some of the more persistent areas of deep convection south of the analyzed storm center.

GOES-16 “Clean” Infrared Window (10.35 µm) images (with and without an overlay of GLM Flash Extent Density) images [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images, with an overlay of GLM Flash Extent Density [click to play animation | MP4]

===== 26 October Update =====

GOES-16 “Clean” Infrared Window (10.35 µm) images (with and without an overlay of GLM Flash Extent Density) and “Red” Visible (0.64 µm) images [click to play animation | MP4]

GOES-16 “Clean” Infrared Window (10.35 µm) images (with and without an overlay of GLM Flash Extent Density) and “Red” Visible (0.64 µm) images [click to play animation | MP4]

Zeta was upgraded to a Hurricane as of 1910 UTC as it approached the Yucatan Peninsula of Mexico on 26 October — 1-minute GOES-16 Infrared (with and without an overlay of GLM Flash Extent Density) and Visible images (above) showed the period of transition from Tropical Storm to Hurricane. The coldest cloud-top infrared brightness temperature was -95.4ºC near the storm center.

Sea Surface Temperature and Ocean Heat Content images [click to enlarge]

Sea Surface Temperature and Ocean Heat Content images [click to enlarge]

Sea Surface Temperature and Ocean Heat Content images from the CIMSS Tropical Cyclones site (above) showed that Zeta was moving over very warm water, and deep-layer wind shear over the storm was very low (below) — all factors which were favorable for tropical cyclone intensification.

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 22 UTC deep-layer wind shear [click to enlarge]

GOES-16 Longwave Infrared (11.2 µm) images, with contours of 22 UTC deep-layer wind shear [click to enlarge]

Record-setting cold in Montana

October 25th, 2020 |

Suomi NPP VIIRS Infrared Window (11.45 µm) and Topography images [click to enlarge]

Suomi NPP VIIRS Infrared Window (11.45 µm) and Topography images [click to enlarge]

A toggle between Suomi NPP VIIRS Infrared Window (11.45 µm) and Topography images (above) showed a pocket of cold air exhibiting a minimum infrared brightness temperature of -35.2ºC (-31.4ºF) in the vicinity of Potomac, Montana at 0915 UTC (3:15 am MDT) on 25 October 2020 — the overnight low air temperature at Potomac was -29ºF, which turned out to be the coldest officially observed air temperature for this early in the winter season for the Lower 48 states.



According to the NOHRSC site, Potomac had a snow depth of 18 inches that morning (below).