Hurricane Force low in the West Pacific

January 10th, 2019 |
GOES-17

GOES-17 “Red” Visible (0.64 µm) images [click to play animation | MP4]

* GOES-17 images shown here are preliminary and non-operational *

GOES-17 “Red” Visible (0.64 µm) images (above) revealed the low-level circulation of an occluded Hurricane Force low (surface analyses) over the West Pacific Ocean on 09 January – 10 January 2019. This storm was forecast to produce wave heights up to 40-60 feet.

GOES-17 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (below) showed the circulation of the storm at higher altitudes.

GOES-17 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation | MP4]

GOES-17 Low-level (7.3 µm, left), Mid-level (6.9 µm, center) and Upper-level (6.2 µm, right) Water Vapor images [click to play animation | MP4]

Metop-A ASCAT surface scatterometer wind speeds were as high as 67 knots southwest of the storm center and 63 knots to the northeast (below).

GOES-17 Mid-level Water Vapor (6.9 µm) image with Metop-A ASCAT surface scatterometer winds [click to enlarge]

GOES-17 Mid-level Water Vapor (6.9 µm) image with Metop-A ASCAT surface scatterometer winds [click to enlarge]

A toggle between VIIRS True Color Red-Green-Blue (RGB) and Infrared Window (11.45 µm) images from Suomi NPP and NOAA-20 — as viewed using RealEarth — is shown below.

NOAA-20 VIIRS True Color and Infrared Window (11.45 µm) images [click to enlarge]

NOAA-20 VIIRS True Color and Infrared Window (11.45 µm) images [click to enlarge]

Southern US storm, and a Tehuano wind event

December 15th, 2018 |

GOES-16 Low-level Water Vapor (7.3 µm) images, 13-15 December [click to play MP4 animation]

GOES-16 Low-level Water Vapor (7.3 µm) images, 13-15 December [click to play MP4 animation]

A large midlatitude cyclone moved from the southern High Plains to the Lower Mississippi Valley during the 13 December15 December 2018 period (surface analyses) — GOES-16 (GOES-East) Low-level Water Vapor (7.3 µm) images (above) showed the evolution of this system.

The corresponding GOES-16 Water Vapor images with plots of hourly surface wind gusts are shown below; peak wind gusts exceeding 50 knots occurred in parts of Colorado, New Mexico and Texas on 13 December.

GOES-16 Low-level Water Vapor (7.3 µm) images with hourly plots of surface wind gusts, 13-15 December [click to play MP4 animation]

GOES-16 Low-level Water Vapor (7.3 µm) images with hourly plots of surface wind gusts in knots, 13-15 December [click to play MP4 animation]

This event was unusually windy in South Texas and the Rio Grande Valley:

Another notable aspect of this storm was a very localized area of heavy snowfall just south of Sweetwater, Texas:


The remnant patch of snow cover was evident in VIIRS Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) imagery on 14 and 15 December (below). The heaviest snowfall occurred over an isolated ridge along the eastern edge of the Edwards Plateau, where elevations of 2500-2600 feet were about 500 feet higher than the adjacent rolling plains. Since snow is a very effective absorber of energy at the 1.61 µm wavelength, it appeared dark on the Snow/Ice imagery.

Topography, Suomi NPP VIIRS Visible (0.64 µm) and Near-Infrared "Snow/Ice" (1.61 µm) images on 14 December [click to enlarge]

Topography plus Suomi NPP VIIRS Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images on 14 December [click to enlarge]

Topography plus NOAA-20 VIIRS Visible (0.64 µm) and Near-Infrared "Snow/Ice" (1.61 µm) images on 15 December [click to enlarge]

Topography plus NOAA-20 VIIRS Visible (0.64 µm) and Near-Infrared “Snow/Ice” (1.61 µm) images on 15 December [click to enlarge]

The residual snow cover on 14 December was also seen in Terra/Aqua MODIS True Color and False Color Red-Green-Blue (RGB) images, viewed using RealEarth (below). The snow appeared as shades of cyan in the False Color images.

Terra/Aqua MODIS True Color and False Color images on 14 December [click to enlarge]

Terra/Aqua MODIS True Color and False Color images on 14 December [click to enlarge]

A toggle between Terra MODIS True Color RGB images on the late morning of 14 and 15 December (below) demonstrated the amount of snow melt in 24 hours.

Terra MODIS True Color RGB images on 14 and 15 December [click to enlarge]

Terra MODIS True Color RGB images on 14 and 15 December [click to enlarge]

The strong cold front associated with this storm moved rapidly southward across the western Gulf of Mexico on 14 December (surface analyses), crossing the terrain of the Isthmus of Tehuantepec in southern Mexico and emerging into the Gulf of Tehuantepec as a gap wind (known as a Tehuano wind). A curved rope cloud marking the leading edge of the Tehuano winds was evident on GOES-17 and GOES-16 “Red” Visible (0.64 µm) images (below).

* GOES-17 images shown here are preliminary and non-operational *

GOES-17 (left) and GOES-16 (right)

GOES-17 (left) and GOES-16 (right) “Red” Visible (0.64 µm) images [click to play animation | MP4]

A comparison of GOES-16 Visible imagery from 14 and 15 December (below) showed how far southwestward the gap winds spread out across the Pacific Ocean during those 2 days. Note that on 15 December there were ship reports with wind speeds of 50 knots, at 12 UTC and at 17 UTC.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images with surface and ship reports, 14-15 December [click to play animation | MP4]

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images on 14 and 15 December (below) also showed the progression of the Tehuano wind rope cloud — the hazy signature of dust-laden air within the offshore flow was also apparent on the daytime True Color images.

NOAA-20 VIIRS True Color and Infrared Window (11.45 µm) images on 14 and 15 December [click to enlarge]

NOAA-20 VIIRS True Color RGB and Infrared Window (11.45 µm) images on 14 and 15 December [click to enlarge]

Metop-A and Metop-B ASCAT surface scatterometer winds across the western Gulf of Mexico [click to enlarge]

Metop-A and Metop-B ASCAT surface scatterometer winds across the western Gulf of Mexico [click to enlarge]

On 14 December, a sequence of EUMETSAT Metop-A and Metop-B ASCAT surface scatterometer winds (source) showed the cold front moving southward across the western Gulf of Mexico (above), and also showed the northerly gap wind flow just beginning to emerge into the Gulf of Tehuantepec around 1607 UTC (below).

Metop-A and Metop-B ASCAT surface scatterometer winds across the southern Gulf of Mexico and the Gulf of Tehuantepec [click to enlarge]

Metop-A and Metop-B ASCAT surface scatterometer winds across the far southern Gulf of Mexico and the Gulf of Tehuantepec [click to enlarge]

The plume of dry air being transported southwestward across the Pacific Ocean by the gap winds was apparent on MIMIC Total Precipitable Water images (below). The majority of this dry air was within the surface-850 hPa layer (21 UTC comparison).

MIMIC Total Precipitable Water product (Total column, and Surface-850 hPa layer) [click to play animation]

MIMIC Total Precipitable Water product (Total column, and Surface-850 hPa layer) [click to play animation]

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]

Blowing dust from the Copper River Valley in Alaska

November 1st, 2018 |

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

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

Strong gap winds accelerating out of the Copper River Valley along the southern coast of Alaska were lofting fine particles of glacial silt/sand and transporting those aerosols southwestward across the Gulf of Alaska on 31 October and 01 November 2018. A sequence of NOAA-20 VIIRS True Color Red-Green-Blue (RGB) images viewed using RealEarth (above) showed that the plume was more widespread on 01 November.

A comparison of Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images (below) showed the plume at 2022 UTC on 01 November. The map overlay has been removed from one set of images, to better reveal the dust plume source region. Note that the plume appeared much warmer (darker shades of red)  in the Shortwave Infrared image — this is due to enhanced solar reflectance off the small dust particles. Since airborne dust is generally transparent at longer infrared wavelengths, only the thickest portion of the plume exhibited a subtle signature on the 11.45 µm image.

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm), Shortwave Infrared (3.74 µm) and Infrared Window (11.45 µm) images [click to enlarge]

The surface visibility briefly dropped to 3 miles at Middleton Island (PAMD) around the time of the Suomi NPP VIIRS images. as gusty north-northeasterly winds carried the plume over that location (below). Although Cordova (station identifier PACV) is only about 20 miles northwest of the Copper River Delta, the localized gap winds did not affect that site (where wind speeds were 3 knots or less the entire day).

Time series plot of surface observations at Middleton Island [click to enlarge]

Time series of surface observations at Middleton Island [click to enlarge]

ASCAT surface scatterometer winds (source) from Metop-A and Metop-B (below) showed speeds in the 25-30 knot range where the gap winds were exiting the Copper River Delta.

Metop-A and Metop-B ASCAT surface scatterometer winds [click to enlarge]

Metop-A and Metop-B ASCAT surface scatterometer winds [click to enlarge]

A toggle between Suomi NPP VIIRS Visible (0.64 µm) and Infrared Brightness Temperature Difference (11-12 µm) images (source) at 2204 UTC on 01 November (below) showed a subtle BTD signal within the more dense center portion of the plume, due to the silicate composition of some of the airborne particulate matter.

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Brightness Temperature Difference (11-12 µm) images [click to enlarge]

Suomi NPP VIIRS Visible (0.64 µm) and Infrared Brightness Temperature Difference (11-12 µm) images [click to enlarge]

VIIRS Aerosol Optical Thickness (AOT) products from the eIDEA site (below) revealed larger AOT values on 01 November.

VIIRS Aerosol Optical Thickness product [click to enlarge]

VIIRS Aerosol Optical Thickness product [click to enlarge]

The gap winds were caused by a strong gradient between cold high pressure over Interior Alaska/Yukon and an occluding gale force low pressure system in the Gulf of Alaska (surface analyses: WPC)| OPC). GOES-15 (GOES-West) Visible (0.63 µm) images (below) showed the circulation of the low, and surface observations highlighted the cold air over snow-covered inland areas. While the dust plume was faintly apparent, it did not show up as well with the lower spatial resolution and large viewing angle of GOES-15.

GOES-15 Visible (0.63 µm) images [click to play animation]

GOES-15 Visible (0.63 µm) images [click to play animation]

A similar — though more prolonged and intense — event was noted in October 2016.