Blowing dust in the Arabian Sea

November 3rd, 2018 |

Sequence of daily True Color RGB images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS, covering the period 01-03 November [click to play animation]

Sequence of daily True Color RGB images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS, covering the period 01-03 November [click to play animation]

Strong winds across southern Iran and Pakistan were lofting plumes of blowing sand/dust offshore over the Gulf of Oman and the Arabian Sea during 01 November, 02 November and 03 November 2018 — a sequence of daily composites of True Color Red-Green-Blue (RGB) images from Terra MODIS, Aqua MODIS and Suomi NPP VIIRS from RealEarth (above) showed the increase in dust transport during that 3-day period.

A comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November is shown below.

Comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November [click to play animation]

Comparison of True Color RGB images from Terra MODIS, NOAA-20 VIIRS, Suomi NPP VIIRS and Aqua MODIS on 03 November [click to play animation]

Metop-A and Metop-B ASCAT data (source) showed surface wind speeds in the 20-25 knot range emerging from the coast where plumes of blowing dust were located (below).

Meop ASCAT surface scatteromete winds [click to enlarge]

Meop ASCAT surface scatteromete winds [click to enlarge]

EUMETSAT Meteosat-11 High Resolution Visible (0.8 µm) images from 02 November and 03 November (below) showed the daily evolution of the dust plumes.

Meteosat-11 Visible (0.8 µm) images [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 02 November [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 03 November [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images on 03 November [click to play animation | MP4]

Pyrocumulonimbus cloud in South Africa

October 29th, 2018 |

Meteosat-11 Visible (0.8 µm), Shortwave Infrared (3.92 µm) and Longwave Infrared Window (10.8 µm) images [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm, top), Shortwave Infrared (3.92 µm, center) and Longwave Infrared Window (10.8 µm, bottom) images [click to play animation | MP4]

The Garden Route Fires had been burning since about 24 October 2018 near George along the southern coast of South Africa (media story). On 29 October, EUMETSAT Meteosat-11 High Resolution Visible (0.8 µm), Shortwave Infrared (3.92 µm) and Longwave Infrared Window (10.8 µm) images (above) showed an elongated west-to-east oriented thermal anomaly or fire “hot spot” (red pixels) just northeast of George (station identifier FAGG) on Shortwave Infrared imagery during the hours leading up to the formation of a pyrocumulonimbus (pyroCb) cloud around 1300 UTC. The pyroCb exhibited the characteristic warm (+10 to +15ºC, darker gray enhancement) shortwave infrared cloud-top signature just off the coast at 1315 UTC, — this is due to enhanced solar reflection off ice crystals that are smaller compared to those of conventional thunderstorm tops.

Zooming out a bit to follow the southeastward drift of the pyroCb cloud (below), the coldest cloud-top 10.8 µm infrared brightness temperature (BT) was -61ºC (darker red enhancement) at 1315 UTC — then the cloud tops remained in the -55 to -59ºC range (orange enhancement) for the next 6 hours or so. Leveraging the large difference between cold 10.8 µm and warm 3.92 µm BTs, NRL calculates a pyroCb index, which classified this feature as an “intense pyroCb” (1315 UTC | animation). The coldest 10.8 µm cloud-top BT of -61ºC roughly corresponds to an altitude of 13.5 km based on 12 UTC rawinsonde data from Port Elizabeth (plot | list).

Meteosat-11 Shortwave Infrared (3.92 µm, left) and Longwave Infrared Window (10.8 µm, right) images [click to play animation | MP4]

Meteosat-11 Shortwave Infrared (3.92 µm, left) and Longwave Infrared Window (10.8 µm, right) images [click to play animation | MP4]

Imagery from NOAA-19 at 1420 UTC (courtesy of René Servranckx) also revealed the warm (dark gray) Shortwave Infrared pyroCb signature, along with a minimum cloud-top infrared BT of -58.1ºC (below).

NOAA-19 AVHRR imagery at 1420 UTC [click to enlarge]

NOAA-19 AVHRR imagery at 1420 UTC [click to enlarge]

A Suomi NPP VIIRS True Color Red-Green-Blue (RGB) image at 1230 UTC (below) was about a half hour before the formation of the pyroCb, but it did show a signature of smoke drifting southeastward off the coast.

Suomi NPP VIIRS True Color RGB image [click to enlarge]

Suomi NPP VIIRS True Color RGB image [click to enlarge]

On the following day (30 October), a NOAA-20 VIIRS True Color image (below) showed the classic comma cloud signature of a mid-latitude cyclone south of the coast, with the band of cold-frontal clouds extending northward across Lesotho. Note the thick plume of smoke spreading eastward within the strong post-frontal westerly winds.

NOAA-20 VIIRS True Color RGB image [click to enlarge]

NOAA-20 VIIRS True Color RGB image [click to enlarge]

A time series of of surface observations from George (below) supported the idea of a cold frontal passage: ahead of the front, temperatures rapidly rose to 104ºF/40ºC (with a dew point of 39ºF/4ºC) on 28 October about 1.5 hours prior to the formation of the pyroCb — then strong westerly winds (gusting to 40 knots/21 mps) with rising pressures and falling temperatures followed on 30 October.

Time series plot of of surface observations from George [click to enlarge]

Time series plot of of surface observations from George [click to enlarge]

The pyroCb research community believes that this is the first documented case of a pyroCb on the African continent.

 

Post-Tropical Cyclone Leslie makes landfall in Portugal

October 13th, 2018 |

Aqua MODIS True Color RGB image [click to enlarge]

Aqua MODIS True Color RGB image, with and without surface reports [click to enlarge]

20 days after Leslie initially formed (and 17 days after it underwent extratropical transition), an Aqua MODIS True Color Red-Green-Blue (RGB) image viewed using RealEarth (above) showed the storm at 1419 UTC on 13 October 2018, when it was still classified as a Category 1 Hurricane off the coast of Portugal. The southwest-to-northeast oriented cloud band just west of Leslie was associated with an advancing cold front (surface analyses), which soon began to absorb the tropical cyclone and aid in its extra-tropical transition a few hours prior to landfall.

EUMETSAT Meteosat-11 middle/upper-tropospheric Water Vapor (6.25 µm) images (below) exhibited a warm/drying trend (brighter shades of yellow) along the western and southern edges of Leslie as it moved inland across Portugal. Hourly Meteosat-11 Water Vapor images visualized using RealEarth are available here.

EUMETSAT Meteosat-11 Water Vapor (6.25 µm) images, with hourly plots of surface winds and gusts in knots [click to play animation | MP4]

EUMETSAT Meteosat-11 Water Vapor (6.25 µm) images, with hourly plots of surface winds and gusts in knots [click to play animation | MP4]

Along the coast of Portugal a thunderstorm was reported at Porto (LPPR) from 1930-2000 UTC (about an hour before landfall). Farther to the south, shortly after landfall the surface winds gusted to 55 knots (63 mph or 28.3 m/s) at Monte Real Air Base (LPMR) at 21 UTC and 42 knots (48 mph or 21.6 m/s) at Ovar Military Base (LPOV) at 23 UTC. The highest wind gust was 95 knots (110 mph or 49 m/s) at Figueira da Foz, located along the coast between LPMR and LPOV:

Meteosat-11 lower/middle-tropospheric Water Vapor (7.35 µm) images (below) revealed the characteristic “scorpion tail” signature of a Sting Jet (Monthly Weather Review | Wikipedia), along with a mesoscale region of warming/drying (darker shades of orange) driven by strong subsidence — this subsidence feature corresponded well with the report of strong winds at Figueira da Foz. Further discussion of this sting jet event is available here.

Meteosat-11 Water Vapor (7.35 µm) images, with hourly splots of surface winds and gusts in knots [click to play animation | MP4]

EUMETSAT Meteosat-11 Water Vapor (7.35 µm) images, with hourly plots of surface winds and gusts in knots [click to play animation | MP4]

Radar composites from the Portuguese Institute for Sea and Atmosphere (IPMA) confirmed that post-tropical cyclone Leslie made landfall around 2100 UTC (below).

Radar reflectivity composites [click to play animation]

Radar reflectivity composites [click to play animation]

Although the view from GOES-16 (GOES-East) was very oblique, the warm/dry signature around the western and southern edges of the storm was still evident on Mid-level Water Vapor (6.9 µm) imagery (below).

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly plots of surface winds and gusts in knots [click to play animation | MP4]

GOES-16 Mid-level Water Vapor (6.9 µm) images, with hourly plots of surface winds and gusts in knots [click to play animation | MP4]

The entire life cycle of Leslie — from becoming a named Subtropical Storm at 15 UTC on 23 September to making landfall as a post-tropical cyclone in Portugal at 21 UTC on 13 October — is shown with 15-minute GOES-16 “Clean” Infrared Window (10.3 µm)  and Mid-level Water Vapor (6.9 µm) images (below). Note that 5-minute imagery was available on 01 October, when GOES-16 was performing a test of the Mode 4 scan strategy.

GOES-16

GOES-16 “Clean” Infrared Window (10.3 µm) images [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]

GOES-16 Mid-level Water Vapor (6.9 µm) images [click to play MP4 animation]



Medicane “Zorbas”

September 29th, 2018 |

NOAA-20 and Suomi NPP VIIRS Day/Night Band (0.7 µm) images [click to enlarge]

NOAA-20 and Suomi NPP VIIRS Day/Night Band (0.7 µm) images [click to enlarge]

Medicane “Zorbas” — as named by Freie Universität Berlin (surface analyses) — developed in the Mediterranean Sea late in the day on 27 September 2018. A toggle between VIIRS Day/Night Band (0.7 µm) images from NOAA-20 and Suomi NPP (above; courtesy of William Straka, CIMSS) revealed the well-defined circulation of the storm a few hours after Midnight local time on 28 September. Note the bright streak north of the storm center on the NOAA-20 image — this was an area of clouds illuminated by intense lightning activity. Other less prominent lightning streaks were evident in thunderstorms farther to the east over the Mediterranean Sea. On the Suomi NPP image, a small bright spot could be seen, evidence of minor volcanic activity at Mount Etna on the island of Sicily, as well as the hazy signature of a plume of blowing dust/sand that was moving northward off the coast of Libya. The corresponding VIIRS Infrared images are available here.

During the following daylight hours of 28 September, EUMETSAT Meteosat-11 High Resolution Visible (0.8 µm) images (below) showed the storm as it became better organized and increased intensity. Another dense plume of blowing dust/sand began to move off the coast of Libya late in the day.

Meteosat-11 Visible (0.8 µm) images, with hourly plots of wind barbs (yellow) and wind gusts (red) [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images, with hourly plots of wind barbs (yellow) and wind gusts (red) [click to play animation | MP4]

On 29 September, Meteosat-11 Visible (0.8 µm) images (below) showed the Medicane moving inland along the Peloponnese coast of southern Greece — shortly after the storm center passed, winds gusted to 48 knots at Kalamata at 1220 UTC (while a heavy thunderstorm was being reported).

Meteosat-11 Visible (0.8 µm) images, with hourly plots of winds (yellow) and gusts in knots (red) [click to play animation | MP4]

Meteosat-11 Visible (0.8 µm) images, with hourly plots of wind barbs (yellow) and gusts in knots (red) [click to play animation | MP4]

A sequence of Terra and Aqua MODIS True Color Red-Green-Blue (RGB) images from 28 and 29 September from RealEarth (below) showed another view of the Zorbas on those 2 days (the valid time of the Terra MODIS image showing the eye-like feature on 29 September was 0911 UTC). Sea Surface Temperatures were near 25ºC in the central Mediterranean Sea where Zorbas was intensifying.

Terra/Aqua MODIS True Color RGB images on 28 and 29 September [click to enlarge]

Terra/Aqua MODIS True Color RGB images on 28 and 29 September [click to enlarge]

Hourly images of the MIMIC Total Precipitable Water product (below) showed moisture associated with the storm, which produced heavy rainfall and flash flooding in parts of southern Greece — the NESDIS Blended TPW Anomaly product indicated that this moisture was as much as 200% of normal for the region and date. Additional information and videos can be found here.

MIMIC morphed Total Precipitable Water images, 27-29 September [click to play animation | MP4]

MIMIC morphed Total Precipitable Water images, 27-29 September [click to play animation | MP4]