Tehuano gap wind event

February 27th, 2020 |

GOES-16 Visible (0.64 µm) images, with plots of surface reports (yellow), ASCAT winds (violet) and surface analyses (cyan) [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images, with plots of surface reports (yellow), ASCAT winds (violet) and surface analyses (cyan) [click to play animation | MP4]

GOES-16 (GOES-East) Visible (0.64 µm) images (above) revealed a cloud arc which marked the leading edge of a Tehuano wind event — air behind a cold front plunged southward across the Gulf of Mexico during the previous day, crossed the mountains of Mexico through Chivela Pass (topography) , and emerged over the Pacific Ocean on 27 February 2020. Within the western portion of the gap wind flow, ASCAT winds speeds were as high as 32 knots at 1540 UTC — but closer to the coast the Ocean Prediction Center was initially forecasting an area of Storm Force winds (downgraded to Gale Force winds later in the day).

On a GOES-16 Visible image with plots of available NOAA-20 NUCAPS profiles (below), the location of one profile immediately offshore (Point 1) and another just ahead of the Tehauno cloud arc (Point 2) are highlighted.

GOES-16 Visible (0.64 µm) image, with plots of available NOAA-20 NUCAPS profiles [click to enlarge]

GOES-16 Visible (0.64 µm) image, with plots of available NOAA-20 NUCAPS profiles [click to enlarge]

A toggle between the NUCAPS profile immediately offshore (Point 1, at 15.39 N latitude 94.55 W longitude) and the profile just ahead of the Tehauno cloud arc (Point 2, at 7.29 N latitude 93.95 W longitude) is show below. Note that Total Precipitable Water values were 1.78 inches ahead of the cloud arc, compared to 1.16 inches immediately off the coast of Mexico where the dry gap winds were entering the Gulf of Tehuantepec.

NOAA-20 NUCAPS Temperature (red) and dewpoint (green) profiles for Point 1 and Point 2 [click to enlarge]

NOAA-20 NUCAPS Temperature (red) and dewpoint (green) profiles for Point 1 and Point 2 [click to enlarge]

In a comparison of Visible images from GOES-17 (GOES-West) and GOES-16 (GOES-East), haziness in the Gulf of Tehuantepec (best seen with GOES-16, due to a larger forward scattering angle) highlighted blowing dust that was being carried offshore by the strong gap winds.

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

GOES-16 True Color Red-Green-Blue (RGB) images created using Geo2Grid (below) provided a clearer view of the blowing dust plumes in the Gulf of Tehuantepec.

GOES-16 True Color RGB images [click to play animation | MP4]

GOES-16 True Color RGB images [click to play animation | MP4]

VIIRS True Color RGB images from Suomi NPP and NOAA-20 as viewed using RealEarth are shown below.

VIIRS True Color RGB images from Suomi NPP and NOAA-20 [click to enlarge]

VIIRS True Color RGB images from Suomi NPP and NOAA-20 [click to enlarge]

Tropical Invest 96P and Tropical Cyclone Vicky near American Samoa

February 18th, 2020 |

GOES-17

GOES-17 “Clean” Infrared Window (10.35 µm) images, 16-18 February [click to play animation | MP4]

GOES-17 (GOES-West) “Clean” Infrared Window (10.35 µm) images (above) showed the movement of numerous thunderstorms across American Samoa during the 16-18 February 2020 period. This deep convection was being forced by an active South Pacific Convergence Zone or “Monsoon Trough” (surface analysis) and the presence of Tropical Invest 96P (named TD07F by the Fiji Met Service / Nadi Tropical Cyclone Centre) northwest of Samoa. Due to outflow from a nearby thunderstorm, winds gusted to 60 knots at Pago Pago, American Samoa (NSTU) at 11 UTC on 17 February.

With an increasing probability of Invest 96P becoming better organized (aided by low values of deep-layer wind shear along with modest upper-level divergence), a GOES-17 Mesoscale Domain Sector was positioned over the Samoan Islands on 18 February — providing “Red” Visible (0.64 µm) and “Clean” Infrared Window images at 1-minute intervals (below). During this period, the coldest convective overshooting tops exhibited infrared brightness temperatures in the -80 to -85ºC range (which corresponded to the tropopause temperatures seen in Pago Pago rawinsonde data).

GOES-17 "Red" Visible (0.64 µm) and "Clean" Infrared Window (10.35 µm) images, 18 February [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images with surface plots for Pago Pago, American Samoa on 18 February [click to play animation | MP4]

===== 20 February Update =====

 GOES-17 "Red" Visible (0.64 µm) and "Clean" Infrared Window (10.35 µm) images with surface plots for Pago Pago, American Samoa on 18 February [click to play animation | MP4]

GOES-17 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images with surface plots for Pago Pago, American Samoa on 20 February [click to play animation | MP4]

Another tropical depression (Invest 97P/TD09F) developed along the active Monsoon Trough on 20 February (surface analyses), intensifying just south of American Samoa to become Tropical Cyclone Vicky (TC 17P) as of 18 UTC (JTWC advisory). Once again a GOES-17 Mesoscale Sector was positioned over the region — “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed the gradual organization of Vicky; the coldest cloud-top infrared brightness temperature of convective overshooting tops was -90ºC. Surface observations revealed a wind gust to 65 knots at Pago Pago, American Samoa just before 20 UTC.

GOES-17 Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Vicky was moving through an environment characterized by of low values of Deep Layer Wind Shear, a favorable factor for further intensification.

GOES-17 Infrared Window (11.2 µm) images with contours of Deep Layer Wind Shear (click to enlarge]

GOES-17 Infrared Window (11.2 µm) images with contours of Deep Layer Wind Shear [click to enlarge]

Hourly MIMIC Total Precipitable Water images during the 16-20 February period (below) displayed the northwest-to-southeast oriented band of elevated moisture along the South Pacific Convergence Zone (or Monsoon Trough). The Samoan Islands are centered near 14.3° S latitude, 170.1° W longitude.

Hourly MIMIC Total Precipitable Water product during the 16-20 February period [click to play animation | MP4]

Hourly MIMIC Total Precipitable Water product during the 16-20 February period [click to play animation | MP4]

Gravity waves over the Gulf of Mexico and Florida

January 22nd, 2020 |

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with pilot reports of turbulence [click to play animation | MP4]

GOES-16 Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images, with pilot reports of turbulence [click to play animation | MP4]

GOES-16 (GOES-East) Low-level (7.3 µm), Mid-level (6.9 µm) and Upper-level (6.2 µm) Water Vapor images (above) showed a packet of gravity waves over the eastern Gulf of Mexico and southern Florida on 22 January 2020. Later time in the time period, there were isolated pilot reports of moderate turbulence in the vicinity of the waves (though it’s uncertain whether the gravity waves were directly responsible).

What caused these gravity waves to form and slowly propagate southeastward is also uncertain — earning this example its place in the “What the heck is this?” blog category. The SPC Mesoscale Analysis at 07 UTC (below) did show weak convergence of 300 hPa ageostrophic winds (dark blue oval) in the entrance region of a secondary jet streak “J” over the Gulf of Mexico — this convergence could have played a role in the gravity wave development.

SPC Mesoscale Analysis valid at 07 UTC, showing 300 hPa height, isotachs and ageostrophic winds [click to enlarge]

SPC Mesoscale Analysis valid at 07 UTC, showing 300 hPa height, isotachs and ageostrophic winds [click to enlarge]

GOES-16 Derived Motion Winds (calculated using 6.9 µm imagery) in the vicinity of the gravity waves (below) had velocities in the 50-60 knot range at pressure levels of 370-380 hPa (0916 UTC).

GOES-16 Water Vapor (6.2 um) Derived Motion Winds [click to enlarge]

GOES-16 Water Vapor (6.9 µm) Derived Motion Winds [click to enlarge]

Also of note was the fact that the surface of southern Florida was sensed by GOES-16 Low-level Water Vapor imagery (below).

GOES-16 Low-level (7.3 µm) Water Vapor images, with pilot reports of turbulence [click to play animation | MP4]

GOES-16 Low-level (7.3 µm) Water Vapor images, with pilot reports of turbulence [click to play animation | MP4]

With an unseasonably cold, dry air mass moving southward over the peninsula, the 7.3 µm water vapor weighting functions were shifted to lower altitudes at Miami and Key West (below) — this allowed the thermal contrast between relatively cool land surfaces and the surrounding warmer water to be seen in the 7.3 µm imagery.

GOES-16 weighting functions for the 7.3 µm (violet), 6.9 µm (blue) and 6.2 µm (green) Water Vapor spectral bands, calculated using 12 UTC rawinsonde data from Miami, Florida [click to enlarge]

GOES-16 weighting functions for the 7.3 µm (violet), 6.9 µm (blue) and 6.2 µm (green) Water Vapor spectral bands, calculated using 12 UTC rawinsonde data from Miami, Florida [click to enlarge]

GOES-16 weighting functions for the 7.3 µm (violet), 6.9 µm (blue) and 6.2 µm (green) Water Vapor spectral bands [click to enlarge]

GOES-16 weighting functions for the 7.3 µm (violet), 6.9 µm (blue) and 6.2 µm (green) Water Vapor spectral bands, calculated using 12 UTC rawinsonde data from Key West, Florida [click to enlarge]

In fact, at Key West the Total Precipitable Water value of 0.3 inch calculated from 12 UTC rawinsonde data (below) was a new record for the date/time (the previous record minimum value was 0.36 inch).

Climatology of Total Precipitable Water for the Key West, Florida rawinsonde site [click to enlarge]

Climatology of Total Precipitable Water for the Key West, Florida rawinsonde site [click to enlarge]

Tropical Cyclone Tino in the South Pacific Ocean

January 16th, 2020 |

Himawari-8

Himawari-8 “Clean” Infrared Window (10.4 µm) images [click to play animation | MP4]

JMA Himawari-8 “Clean” Infrared Window (10.4 µm) images (above) showed the development of Tropical Cyclone Tino in the South Pacific Ocean on 16 January 2020. Tino was moving southeast toward the island nation of Fiji. Convection around the tropical cyclone exhibited extensive cloud-top infrared brightness temperatures (IRBTs) of -90ºC and colder (shades of yellow embedded within the dark purple enhancement), including a few red -100ºC pixels at 1630 UTC.

Plots of rawinsonde data from Fiji (below) showed a tropopause around 100 hPa, where the temperature was around -85ºC — so the tropical overshooting tops with IRBTs in the -90 to -100ºC range were extending into the stratosphere.

Plots of rawinsonde data from Fiji [click to enlarge]

Plots of rawinsonde data from Nandi, Fiji [click to enlarge]

Plots of deep-layer wind shear from the CIMSS Tropical Cyclones site (below) indicated that Tino gradually intensified within a narrow zone of light shear.

Plots of deep-layer wind shear [click to enlarge]

Plots of deep-layer wind shear [click to enlarge]

===== 17 January Update =====

GOES-17

GOES-17 “Clean” Infrared Window (10.35 µm) images [click to play animation | MP4]

A GOES-17 (GOES-West) Mesoscale Domain Sector was positioned over Tropical Cyclone Tino on 17 January, providing images at 1-minute intervals — “Clean” Infrared Window (10.35 µm) images (above) showed the continued development of convective bursts, which at times exhibited IRBT values as cold as -100ºC (red pixels on the coldest portion of the enhancement).