Medicane approaching Greece

September 17th, 2020 |

Daily VIIRS True-Color images over the central Mediterranean Sea, 14 – 19 September 2020 (Click to enlarge)

A Medicane (a portmanteau of Mediterranean and Hurricane) has developed in the central Mediterranean Sea, and moved northeastward through the Ionian Sea towards Greece and Albania. Daily snapshots of VIIRS true-color imagery, above, from NASA Worldview, show a slow increase in organization. (Previous CIMSS Blog Posts on Medicanes are here, here and here.) This Medicane was given the name ‘Ianos’.

There is an isolated region of small values of wind shear over this system (1800 UTC image from 17 September, from this website), as expected for a tropical storm.  An image of hourly CMORPH precipitation values, below, show heavy precipitation associated with the storm as well.

CMORPH Hourly Precipitation ending 1700 UTC on 17 September 2020 (Click to enlarge)

The ASCAT instrument on Metop-B observed a very tight cyclonic circulation on 16 September, as shown below (imagery from this site).

Metop-B ASCAT winds, 16 September 2020 (Click to enlarge)

MIMIC Total Precipitable Water (TPW) (below, from this site) shows a compact swirl around the storm, with large values of TPW.

MIMIC Total Precipitable Water for the 24 hours ending 2000 UTC on 17 September 2020 (click to enlarge)


NASA’s IMERG product showed the heavy rain that was associated with this storm as it moved towards Greece.

CMORPH estimates of hourly (and daily) rainfall with Sally

September 16th, 2020 |

CMORPH hourly estimates of precipitation over Mississippi and surrounding states, 1300-2200 UTC 16 September 2020 (Click to enlarge)

Hurricane Sally weakened to a Tropical Storm at 1800 UTC on 16 September. Sally is a prodigious rainfall producer. CMORPH (CPC Morphing Technique) Precipitation estimates (blogged about earlier) are available at this Real Earth website. Hourly estimates from 1300 through 2200 UTC are shown above.  Many locations over southern Mississippi show hourly multi-inch accumulations for much of the day.

Daily precipitation for the 24 hours ending at 00 UTC on 17 September is shown below.  A large area of Mississippi shows values between exceeding 100-150 mm.  Click here to see a 24-h precipitation total image for the period ending 1200 UTC on 17 September (from this website) A series of daily images of 24-hour precipitation (at bottom) shows the evolution of the diagnosed precipitation from 09-16 September.

Daily CMORPH Precipitation Accumulation, valid 0000 UTC on 17 September 2020 (Click to enlarge)

Daily CMORPH estimates of precipitation, 09-16 September 2020 (Click to enlarge)

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.

 width=

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)