Tropical Storm Claudette makes landfall along the central Gulf Coast

June 19th, 2021 |

MIMIC Total Precipitable Water (TPW) estimates, 1900 UTC 18 June 2021 – 1800 UTC 19 June 2021 (Click to enlarge)

The Potential Tropical Cyclone that has been moving northward through the Gulf of Mexico made landfall southwest of New Orleans, LA on Saturday 19 June as a minimal Tropical Cyclone. The animation of total precipitable water, above, from the MIMIC TPW website, shows that most of the storm’s moisture is east of the center. (The circulation of Pacific Tropical Storm Dolores is also apparent, making landfall near Punta San Telmo in Mexico) A percent-of-Normal plots from NOAA/NESDIS/OSPO, below, shows values about 150% of normal over much of the southeast USA. Consequently, Flash Flood Watches are in effect over much of southern Alabama northeastward into western North Carolina, as shown below.

Percent-of-normal Blended Total Precipitable Water, 1800 UTC on 19 June 2021 (Click to enlarge)

Weather hazards at 1911 UTC on 19 June 2021 (Click to enlarge)

A True-Color image from CSPP Geosphere, below, taken from this link, shows the storm inland over southwestern Alabama; much of the rain and deep moisture with the storm remains to the east of the center.

True-Color imagery, 1921 UTC on 19 June 2021, from CSPP Geosphere (Click to enlarge)

Potential Tropical Cyclone 3 in the Gulf of Mexico

June 17th, 2021 |

GOES-16 “Red” Visible (0.64 µm) and

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

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 formation of Potential Tropical Cyclone 3 in the Gulf of Mexico on 17 Jun 2021. A low-level circulation could be seen near the storm center on Visible imagery, but deep convection was only occurring at some distance from the center.

Even though the tropical disturbance was forming over warm waters (SST | OHC), a plot of modest to high amounts of deep-layer wind shear from the CIMSS Tropical Cyclones site (below) indicated that the rate of intensification might be relatively slow.

 GOES-16 Infrared Window images, with contours of deep-layer wind shear [click to enlarge]

GOES-16 Infrared Window images, with contours of deep-layer wind shear [click to enlarge]

PTC3 is expected to develop into Tropical Storm Claudette on 18 June — at which point this blog post will be updated.

Rapid Convective Initiation and NUCAPS Profiles in the upper Midwest

June 17th, 2021 |

NUCAPS Sounding Availability, 1745 and 1927 UTC on 17 June 2021. Note the overlapping coverage in eastern Iowa (Click to enlarge)

A favorable orbit geometry on NOAA-20 on 17 June 2021 meant that portions of the upper Midwest received NUCAPS soundings 90 minutes apart. This is an ideal way to monitor destabilization on a day when SPC has predicted an enhanced risk of severe weather, as shown below and at this link.

SPC Convective outlook, 2000 UTC on 17 June 2021 (Click to enlarge)

Compare the sounding at 42º N, 92º W from ~1800 UTC to the one from ~1930 UTC, below.  Destabilization is apparent;  the later profile has a lower LCL and lower LFC, and moisture has increased.

NUCAPS Profiles near 42º N, 92º W at 1800 and 1930 UTC, 17 June 2021 (Click to enlarge)

This surface plot from 2000 UTC suggests that the NUCAPS profile at ~1930 UTC has a boundary layer that is too cool and too dry.  When the sounding values are edited — the lowest 3 layers were warmed and moistened — to better match the plotted observations, the sounding CAPE increased, and the LCL/LFC dropped even farther.

Original and modified NUCAPS profile at 42.14ºº N, 91.54 W, ~1930 UTC on 17 June 2021 (Click to enlarge)

The convection developed rapidly.  The every-90-minutes toggle below (GOES-16 Visible Imagery at 2000, 2130, 2300 UTC) shows that, and the Day Cloud Phase Distinction RGB at the bottom (from 1901-2356 UTC) does too.

GOES-16 Band 2 Visible (0.64 µm) Imagery, 2001, 2136, 2301 UTC on 17 June 2021 (Click to enlarge)

GOES-16 Day Cloud Phase Distinction RGB, 1901 – 2306 UTC on 17 June 2021 (Click to animate)

A low-level water vapor (GOES-16 Band 10, 7.3 µm) infrared imagery animation, below, from CSPP Geosphere (here is a link that will show the animation in CSPP GeoSphere until about the end of June), shows evidence of a northwestward-propagating gravity wave that might have initiated convection.  This feature first interacts with convection over far southeastern Iowa, and then with a southwest-to-northeast line of convection that developed.

Lake Surface Temperatures in the Great Lakes in mid-June

June 16th, 2021 |

Lake-surface temperatures over the Great Lakes, 0747 UTC on 16 June 2021

Mostly clear skies over the Great Lakes early in the morning on 16 June allowed the VIIRS instrument on Suomi-NPP an unobstructed view of the surface waters.  Advanced Clear-Sky Processing for Oceans (ACSPO) Lake-surface temperatures, above, show the temperature distributions in the five lakes.  The warmest region is western Lake Erie where water temperatures are already in the 70s.  Saginaw Bay in Lake Huron (and Green Bay in Lake Michigan — although clouds at this time prevented a good view) are also in the 70s.  Much of Lake Superior remains around 40 F;  Lake Michigan is unusually warm — with a large region of 60+ — following an early-season heat wave (graph from GLERL’s Lake Statistics webpage).

Clear skies continued into the afternoon of the 16th;  the true-color image, below, derived from VIIRS data from NOAA-20 shows cloud over Lake Huron and some sun glint over Lakes Michigan and Superior. A zoomed-in view of Lake Erie (link) shows remarkable detail to the water color in the lake.

VIIRS True-Color image over the Great Lakes, 1819 UTC on 16 June 2021 (Click to enlarge)

Suomi-NPP and NOAA-20 VIIRS data were downloaded at the CIMSS Direct Broadcast site and processed using CSPP software. Great Lakes SST fields and VIIRS imagery over CONUS are available via LDM feed to National Weather Service Offices. True-Color imagery can be found at VIIRS Today and at the CIMSS direct broadcast ftp site.