Tropical Invest 90L becomes Subtropical Storm Ana in the Atlantic

May 21st, 2021 |

GOES-16 Visible and Infrared images [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [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 (above) displayed the exposed low-level circulation of Invest 90L, in the Atlantic Ocean (about 150 miles northeast of Bermuda, TXKF) on 21 May 2021.

GOES-16 Visible images with plots of Visible Derived Motion Winds (below) revealed a few wind speeds of 50 knots or greater (red wind barbs) within its northwest quadrant — but since no organized and sustained deep convection remained in close proximity to the low-level circulation, Invest 90L was not yet considered to be a tropical cyclone.

GOES-16

GOES-16 “Red” Visible (0.64 µm) images, with plots of Visible GOES-16 Derived Motion Winds [click to play animation | MP4]

===== 22 May Update =====

GOES-16 "Clean" Infrared Window (10.35 µm) images [click to play animation | MP4]

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

During the overnight hours, convection organized and intensified around the low-level circulation of Invest 90L — and as of 0900 UTC it was classified as Subtropical Storm Ana. GOES-16 Infrared images of Ana are shown above.

A closer view of GOES-16 Visible images (below) indicated that the center of Ana eventually stopped moving southwestward toward Bermuda, performed a counterclockwise loop, then began moving to the northeast.

GOES-16 "Red" Visible (0.64 µm) images [click to play animation | MP4]

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

GOES-16 Visible images with plots of Derived Motion Winds (below) indicated that the maximum near-surface wind speeds were 39 knots.

GOES-16 "Red" Visible (0.64 µm) images, with plots of Derived Motion Winds [click to play animation | MP4]

GOES-16 “Red” Visible (0.64 µm) images, with plots of Visible GOES-16 Derived Motion Winds [click to play animation | MP4]

GOES-16 "Red" Visible (0.64 µm) images, with plots of Metop-A ASCAT winds [click to enlarge]

GOES-16 “Red” Visible (0.64 µm) image at 1219 UTC, with plots of Metop-A ASCAT winds [click to enlarge]

An overpass of Metop-A at 1219 UTC provided ASCAT surface scatterometer winds centered on Ana (above), with a maximum speed value of 31 knots just northwest of the storm center. In general, Visible GOES-16 Derived Motion Wind speed values were around 5 knots faster than nearby ASCAT winds (below) — since the former are computed by tracking cloud targets that are above the surface, where winds speeds are greater (due to a lack of surface friction).

GOES-16 "Red" Visible (0.64 µm) image at 1219 UTC, with plots of Visible GOES-16 Derived Motion Winds and Metop-A ASCAT winds [click to enlarge]

GOES-16 “Red” Visible (0.64 µm) image at 1219 UTC, with plots of Visible GOES-16 Derived Motion Winds and Metop-A ASCAT winds [click to enlarge]

Subtropical Storm Potira off the coast of Brazil

April 20th, 2021 |

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

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

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) images (above) showed the circulation of Subtropical Storm Potira (warning issued by MARINHA) off the southeast coast of Brazil on 20 April 2021.

In the corresponding 1-minute GOES-16 “Clean” Infrared Window (10.35 µm) images (below), intermittent convective overshooting tops exhibited infrared brightness temperatures as cold as -60 to -65ºC (shades of orange).

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

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

Combined plots of all GOES-16 Atmospheric Motion Vector types — Visible, Infrared and Water Vapor — and pressure levels at 15-minute intervals (below) displayed the cloud motions of Potira (credit: Dave Stettner and Chris Velden, CIMSS). The algorithm used to generate these AMVs differs slightly from that used to create operational Derived Motion Winds: some constraints are relaxed/removed, and Visible winds are calculated at pressure levels above 700 hPa — all of which results in the display of a higher density of tracked targets and their calculated wind vectors.

Combined plot of all GOES-16 Atmospheric Motion Vector types (Visible, Infrared and Water Vapor) at 15-minute intervals [click to play animation | MP4]

Combined plots of all GOES-16 Atmospheric Motion Vector types (Visible, Infrared and Water Vapor) and pressure levels, at 15-minute intervals [click to play animation | MP4]

A sequence of EUMETSAT Metop ASCAT surface scatterometer winds (source) is is shown below — the strongest winds were located within the southern sector of the storm, well away from the center of circulation.

Metop ASCAT surface scatterometer winds [click to enlarge]

Metop ASCAT surface scatterometer winds [click to enlarge]

===== 22 April Update =====

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

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

1-minute GOES-16 Visible images (above) showed that the low-level circulation center of Potira remained exposed on 22 April — while GOES-16 Infrared images (below) indicated that deep convection remained south and west of the storm center.

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

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

Cyclone Habana in the South Indian Ocean

March 10th, 2021 |

US Space Force EWS-G1 Infrared Window (10.7 µm) images [click to play animation | MP4]

US Space Force EWS-G1 Infrared Window (10.7 µm) images [click to play animation | MP4]

US Space Force EWS-G1 Infrared Window (10.7 µm) images (above) displayed the well-defined eye and eyewall structure of Cyclone Habana in the South Indian Ocean on 10 March 2021. This was the second period of Category 4 intensity (ADT | SATCON) during the life cycle of Habana.

Meteosat-8 Infrared images with contours of deep-layer wind shear from the CIMSS Tropical Cyclones site (below) showed that Habana was moving through an environment of relatively low shear.

Meteosat-8 Infrared images, with contours of deep-layer wind shear [click to enlarge]

Meteosat-8 Infrared images, with contours of deep-layer wind shear [click to enlarge]

Meteosat-8 Infrared images with an overlay of 1505 UTC Metop ASCAT winds (below) depicted a fairly uniform distribution of winds within the eyewall region, as Habana developed an annular structure.

Meteosat-8 Infrared images, with a plot of Metop ASCAT winds [click to enlarge]

Meteosat-8 Infrared images, with a plot of Metop ASCAT winds [click to enlarge]

SSMIS Microwave (85 GHz) images from DMSP-16 at 1139 UTC and DMSP-18 at 2327 UTC are shown below.

DMSP-16 SSMIS Microwave (85 GHz) image at 1139 UTC [click to enlarge]

DMSP-16 SSMIS Microwave (85 GHz) image at 1139 UTC [click to enlarge]

DMSP-18 SSMIS Microwave (85 GHz) image at 2327 UTC [click to enlarge]

DMSP-18 SSMIS Microwave (85 GHz) image at 2327 UTC [click to enlarge]

 

Re-suspended ash from the Katmai volcano in Alaska

February 28th, 2021 |

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

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

1-minute Mesoscale Domain Sector GOES-17 (GOES-West) “Red” Visible (0.64 µm) images (above) showed the hazy signature of a plume of re-suspended ash from the 1912 Katmai volcanic eruption. Strong surface winds gusting to 50-55 knots — caused by a strong pressure gradient along the western periphery of a Storm Force low in the Gulf of Alaska (surface analyses) — lofted some of the thick layer of ash that has remained on the ground in the vicinity of the volcano. The most dense portion of the aerosol plume was  moving across the Barren Islands (between Kodiak Island to the south and the Kenai Peninsula to the north); near the northern edge of the aerosol plume, surface visibility was reduced to 5 miles at Homer and 7 miles at Seldovia.

A sequence of Suomi NPP VIIRS Day/Night Band (0.7 µm) images (below) showed that the plume had formed before sunrise — ample illumination from a Full Moon provided vivid “visible mages at night” (at 1131 UTC and 1311 UTC).

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

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

ASCAT winds from Metop-C at 0743 UTC and 2124 UTC (source) are shown below — they indicated a dramatic increase in surface wind speeds  of 50 knots or greater emerging from the Barren Islands into the Gulf of Alaska later in the day.

ASCAT winds from Metop-C, at 0743 UTC and 2124 UTC [click to enlarge]

ASCAT winds from Metop-C, at 0743 UTC and 2124 UTC [click to enlarge]

GOES-17 True Color RGB images created using Geo2Grid (below) provided a clearer view of the re-suspended ash plume. North of the plume, note the tidal ebb and flow of ice within Cook Inlet and Turnagain Arm leading into the Anchorage area.

GOES-17 True Color RGB images [click to play animation | MP4]

GOES-17 True Color RGB images [click to play animation | MP4]