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]

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