Hurricane Sally makes landfall in Alabama

September 16th, 2020 |

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

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

At 0500 UTC on 16 September 2020, Hurricane Sally rapidly intensified (ADT | SATCON) to a Category 2 storm, and soon thereafter made landfall near Gulf Shores, Alabama at 0945 UTC. During that time period, 1-minute GOES-16 Infrared imagery — with and without an overlay of GLM Flash Extent Density (above) — displayed a ragged eye structure, along with a lack of GLM-detected lightning activity in the immediate vicinity of the storm center. The eye passed just to the west of Buoy 42012, where the wind gusted to 95.2 knots or 110 mph at 0510 UTC (below).

Plot of wind speed (blue), wind gusts (red) and pressure (green) at Buoy 42012

Plot of wind speed (blue), wind gusts (red) and pressure (green) at Buoy 42012


How did Sally change the Sea Surface Temperatures (SSTs) in the Northern Gulf? The toggle below of Advanced Clear Sky Processor for Ocean (ACSPO) SSTs from VIIRS, derived using CSPP (the Community Satellite Processing Package) and direct broadcast data at CIMSS, shows SSTs about 2ºF cooler (cyan in the enhancement, about 80ºF) compared to surrounding waters that are 82-83ºF..

ACSPO SSTs at 0746 and 1912 UTC on 17 September 2020 (click to enlarge)

Hurricane Sally

September 15th, 2020 |

GOES-16 Clean Window Infrared (10.3 µm) Imagery over Sally, 1113 – 1312 UTC 14 September 2020. GLM Flash Density (1-minute observations) are also plotted (Click to animate)

Hurricane Sally was moving very slowly in the north-central Gulf of Mexico at sunrise on 15 September 2020. A GOES-16 Mesoscale sector placed over the storm allowed for 1-minute imagery, and the Clean Infrared window animation, above, for the 2 hours centered on Sunrise, show a compact storm south of Mobile Bay and east of the Mississippi River delta. Geostationary Lightning Mapper (GLM) data overlain on the ABI imagery show active lightning in a feeder band to the east of the storm, but little lightning in the storm center.

GOES-16 Upper Level (6,19 µm) and Lower Level (7.34 µm) water vapor imagery, 1311 UTC on 15 September 2020 (Click to enlarge)

Intensification of Sally has been affected by dry air near the storm (as mentioned in this discussion, for example). The toggle above of GOES-16 infrared upper-level and lower-level water vapor imagery (observed at 6.19 µm and 7.34 µm, respectively), shows warm brightness temperatures to the west of the storm.  These warm temperatures (yellow in the 7.34 µm image, blue in the 6.19 µm image) are regions of mid-level dryness:  the top of the moist layer is farther down in the atmosphere in these regions.

Morphed microwave imagery, below, (from this site), shows the effect of dry air on the storm structure.  The eyewall almost forms — but it is eroded along its southern edge by dry air.

Morphed Microwave imagery following the center of Hurricane Sally for the 24 hours ending 1300 UTC on 15 September (Click to enlarge)

The 1200 UTC MIMIC Total Precipitable Water (TPW) field, below (from this site) suggests that dryer Continental air might be affecting the storm.  Advected Layer Precipitation Water from 1200 UTC (here, from this site), tells a similar tale.

Microwave-derived Total Precipitable Water, 1200 UTC on 15 September 2020 (Click to enlarge)

Visible imagery, below, at sunrise shows a thick clouds over the center of the storm.  The appearance is similar to yesterday’s. A visible animation (from 1130-1313 UTC) without the GLM overlay is available here.

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GOES-16 visible imagery (0.64 µm) with 1-minute GLM Flash Density overlain, 1145 – 1311 UTC 15 September (Click to animate)

===== 21 UTC Update =====

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

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (with and without an overlay of GLM Flash Extent Density) [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 — with and without an overlay of GLM Flash Extent Density (above) showed a series of convective bursts that rotated around the center of Category 1 Hurricane Sally during the daylight hours. Minimal GLM-detected lightning activity was seen with these convective bursts.

A toggle between Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images (below) showed Sally at 1806 UTC. The coldest cloud-top infrared brightness temperature northwest of the eye was -86ºC.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 1806 UTC [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Window (11.45 µm) images at 1806 UTC [click to enlarge]

For the latest information on Hurricane Sally, refer to the pages of the National Hurricane Center.  (Direct link to Sally)

Hurricane Sally in the northern Gulf of Mexico

September 14th, 2020 |

Sally was upgraded to a Hurricane at 1600 UTC on 14 September. (Link)

MIMIC total precipitable water, 12 UTC 13 September – 11 UTC 14 September 2020 (Click to enlarge)

Hurricane warning have been issued along the central Gulf Coast on 14 September as strengthening tropical storm Sally approached.  MIMIC estimates of total precipitable water, above, for the 24 hours ending at 11 UTC on 14 September show the moist airmass in the Gulf that is helping to sustain the storm.  (Also apparent in the imagery:  Hurricane Paulette, moving over the island of Bermuda, and Pacific Tropical Storm Karina.  (For more information on these storms (and other storms during this active Atlantic Hurricane Season), and for the latest on Sally, refer to the National Hurricane Center)

Both Suomi NPP and NOAA-20 overflew Sally between 0700 and 0800 UTC on 14 September, and Day Night Band imagery for the storm (source) is shown below. The 50-minute time step between the two images show little because of a lack of lunar illumination, but westward expansion of the cloud shield near the Mississippi River delta is apparent. This suggests adequate upper-level divergence for continued storm intensification.

Suomi NPP (0707 UTC ) and NOAA-20 (0757 UTC) Day Night Band imagery on 14 September 2020 (Click to enlarge)

GOES-16 animations of infrared imagery for the 12 hours endings near 1300 UTC on 14 September, below, also show an expansion in the size of the coldest cloud tops in the storm’s center. A frontal zone is also apparent in the infrared imagery, stretching from New York/Pennsylvania southwestward to north Texas. This front will limit how far north the effects of Sally — post landfall — can move. (The forecast as of 14 September moves the post-landing remnants of Sally through Georgia).

GOES-16 Clean Window Infrared (10.3 µm) Imagery over Sally, 0116 – 1316 UTC 14 September 2020 (Click to animate)

Low-level Water vapor infrared imagery (GOES-16 Band 10, at 7.3 µm; click here for the Upper-level Water vapor infrared imagery, at 6.2 µm), below, using an enhancement courtesy William Churchill, WFO Key West (Click here for the Band 10 animation with a more familiar, perhaps, ‘dry yellow’ enhancement), also shows the expansion of the clouds in the central core of the storm. An apparent outflow channel from the storm south over Cuba also shows up in the animation.

GOES-16 Low-Level water vapor Infrared (7.3 µm) Imagery over Sally, 0926 – 1331 UTC 14 September 2020 (Click to animate)

A GOES-16 mesoscale sector is viewing the development of Sally, allowing for 1-minute imagery.  Visible imagery below, for two hours shortly after sunrise, shows active convection ongoing in the center of the storm and an obvious expansion of the central dense overcast. Both things support strengthening is the inner core structure.

GOES-16 Visible (0.64 µm) imagery, every minute, from 1233 to 1432 UTC on 14 September 2020 (Click to animate)

===== 21 UTC Update =====

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

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (with and without an overlay of GLM Flash Extent Density) [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 — with and without an overlay of GLM Flash Extent Density (above) showed Hurricane Sally after it was upgraded to a Category 2 storm at 21 UTC. A series of convective bursts could be seen developing near the center of Sally; as is usually the case, very little GLM-detected lightning activity was associated with these types of convective bursts located within close proximity to the eye. Winds at Viocsa Knoll — an elevated oil platform, located just northwest of the storm center — gusted to 94 knots or 108 mph at 2100 UTC (shortly after gusting to 102 knots or 117 mph at 2020 UTC).

You can find more information on Sally at the SSEC Tropical Website (Link). For official forecasts, refer to the pages of the National Hurricane Center. Interests along the central Gulf Coast should be preparing for the arrival of this storm, in addition to monitoring its progress.

Pyrocumulonimbus cloud spawned by the Creek Fire in California

September 5th, 2020 |

GOES-17 “Red” Visible (0.64 µm, top left), GOES-17 Shortwave Infrared (3.9 µm, top right), GOES-17 Fire Temperature RGB + GLM Flash Extent Density(bottom left) and

GOES-17 “Red” Visible (0.64 µm, top left), Shortwave Infrared (3.9 µm, top right), Fire Temperature RGB + GLM Flash Extent Density (bottom left) and “Clean” Infrared Window (10.35 µm, bottom right) [click to play animation | MP4]

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm), GOES-17 Shortwave Infrared (3.9 µm), Fire Temperature Red-Green-Blue (RGB) + GLM Flash Extent Density (FED) and “Clean” Infrared Window (10.35 µm) images (above) showed the formation of a pyrocumulonimbus (pyroCb) cloud created by the Creek Fire in Central California on 05 September 2020. The appearance of a few brief GLM FED pixels (2026 UTC | 2117 UTC) indicated that this pyroCb cloud was producing lightning; the coldest cloud-top infrared brightness temperatures were -56.3ºC. The pyroCb developed after the Creek Fire made an explosive run to the north — and the pyroCb also spawned two “fire tornadoes”, which were rated EF2 and EF1 (Wildfire Today).

A comparison of time-matched Infrared Window images of the Creek Fire pyrocumulonimbus cloud from Suomi NPP (SNPP) and GOES-17 (below) highlighted differences in spatial resolution — 375-m with SNPP, vs 2-km (at satellite sub-point) with GOES-17 — and parallax displacement inherent with GOES-17 imagery at that location (17 km for a 15.2-km tall cloud top). The coldest cloud-top infrared brightness temperatures were -71.0ºC with SNPP, vs -55.5ºC with GOES-17. Identical color enhancements were applied to both images.

Infrared Window images from Suomi NPP and GOES-17 [click to enlarge]

Infrared Window images from Suomi NPP (11.45 µm) and GOES-17 (10.35 µm) [click to enlarge]

Several hours later, a nighttime comparison of Suomi NPP VIIRS Day/Night Band (0.7 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images of the Creek Fire at 0935 UTC or 2:35 am PDT (below) showed the bright glow of the large fire, with several small but very hot fires continuing to burn along its periphery — and a few pyrocumulus clouds were developing along the western/southwestern edge. Along the northeastern edge of the fire signature, outlined in blue, is the Mammoth Pool Reservoir — where over 200 people needed to be airlifted from a campground after the only exit road was cut off by the fast-moving fire (media report).

Suomi NPP VIIRS Day/Night Band (0.7 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images

Suomi NPP VIIRS Day/Night Band (0.7 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]