Center-fixing a storm with SAR and SSMIS data

September 23rd, 2022 |
Sentinel SAR Wind Speeds, 0757 UTC on 23 September 2022 (Click to enlarge)

Sentinel overflew Tropical Storm Gaston, northwest of the Azores Islands, shortly before 0800 UTC on 23 September 2022, as shown above. The Beaufort Scale enhancement suggest peak winds derived from SAR observations to be very close to 50 knots in curved bands to the east/southeast of the center, inferred to be just off the edge of observation swath, which is at 40.76o N Latitude, 29.3o W Longitude. GOES-16 satellite imagery spanning this time around sunrise shows an exposed low-level circulation center with stronger convection building along the northern perimeter of the storm (mp4 animation shown here, created with CSPP Geosphere — direct link is here). Because GOES-16 can view the low-level circulation, the parallax shift of the center in the animation is small (smaller than the parallax shift in the SAR/GOES-16 imagery shown here Fiona) even though Gaston is near the satellite limb.

DMSP-17 carries the SSMIS (Special Sensor Microwave Imager/Sensor) and overflew Gaston just after 0900 UTC, as shown below in an image from the SSEC Tropical Website. The estimated wind speed from this image is 52 knots, close to the SAR values shown above. The 0900 UTC update from the National Hurricane Center showed a center at 40.5oN, 29.6oW and maximum sustained windspeeds at 50 knots.

85 GHz observations from SSMIS-17, 0911 UTC on 23 September 2022 (Click to enlarge)

Fiona intensifies to a Category 4 hurricane

September 21st, 2022 |

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animated GIF | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed Fiona as it intensified to a Category 4 Hurricane just east of The Bahamas at 0900 UTC on 21 September 2022. The coldest cloud-top 10.35 µm infrared brightness temperatures were around -81ºC.

GOES-16 Infrared images with and without a overlay of GLM Flash Extent Density (below) did reveal isolated brief periods of lightning in the eyewall region of Fiona — but most of the lightning activity was associated with convection well east of the eye.

GOES-16 “Clean” Infrared Window (10.35 µm) images, with and without a overlay of GLM Flash Extent Density [click to play animated GIF | MP4]

The corresponding 1-minute GOES-16 Cloud Top Temperature and Cloud Top Height derived products are shown below — the coldest Cloud Top Temperature values were around -84ºC, while maximum Cloud Top Height values were around 58,000 feet.

GOES-16 Cloud Top Temperature and Cloud Top Height derived products [click to play animated GIF | MP4]

In a time-matched comparison of Infrared Window images from Suomi-NPP and GOES-16 at 0700 UTC (below), the coldest cloud-top infrared brightness temperatures were -86ºC and -81ºC, respectively. A slight northwestward parallax displacement was evident with the GOES-16 image.

Infrared Window images from Suomi-NPP (11.45 µm) and GOES-16 (10.35 µm) [click to enlarge]

===== 23 September Update =====

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

As Fiona passed just to the northwest of Bermuda during the nighttime hours on 22-23 September, it was briefly downgraded to a Category 3 storm at 0600 UTC (before being again upgraded to Category 4 at 1200 UTC on the following morning) — but a wind gust to 81 knots (93 mph) was recorded at Bermuda Naval Air Station (station identifier TXKF) shortly before 10 UTC while that airport was temporarily closed to air traffic (Bermuda discussion). 1-minute GOES-16 Infrared images (above) showed Fiona during the 0000-1000 UTC period on 23 September.

A DMSP-17 SSMIS Microwave (85 GHz) image at 1053 UTC from the CIMSS Tropical Cyclones site (below) exhibited the eye and eyewall structure about an hour after the peak wind gust at Bermuda.

DMSP-17 SSMIS Microwave (85 GHz) image at 1053 UTC [click to enlarge]

Fiona becomes a Hurricane near Puerto Rico

September 18th, 2022 |

GOES-16 “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images [click to play animated GIF | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) “Red” Visible (0.64 µm) and “Clean” Infrared Window (10.35 µm) images (above) showed Fiona as it intensified to a Category 1 Hurricane just south of Puerto Rico during the morning hours on 18 September 2022. The coldest cloud-top 10.35 µm infrared brightness temperatures were around -88ºC.

The corresponding 1-minute GOES-16 Cloud Top Temperature and Cloud Top Height derived products are shown below — the coldest Cloud Top Temperature values were around -91ºC, while maximum Cloud Top Height values were around 61,000 feet.

GOES-16 Cloud Top Temperature and Cloud Top Height derived products [click to play animated GIF | MP4]

The highest wind gust at Buoy 42085 — located just south of Ponce (station identifier TJPS) — was 72 knots (83 mph) at 16 UTC (below).

Plots of wind speed(blue), gusts (red) and pressure (green) at Buoy 42085 [click to view]

Although Fiona was moving across relatively warm water, GOES-16 Infrared Window (11.2 µm) images with contours of deep-layer wind shear from the CIMSS Tropical Cyclones site (below) indicated that the storm was moving through an environment of moderate shear.

GOES-16 Infrared Window (11.2 µm) images, with contours of deep-layer wind shear valid at 1700 UTC [click to enlarge]

Hurricane Fiona later made landfall in far southwestern Puerto Rico around 1920 UTC — a DMSP-18 image at 2013 UTC (below) showed the eye as it was beginning to move into the Mona Passage.

DMSP-18 SSMIS Microwave (85 GHz) image at 2013 UTC [click to enlarge]

A prolonged period of strong winds and heavy rainfall from Fiona led to widespread power outages and flash flooding across much of Puerto Rico.

Super Typhoon Hinnamnor in the West Pacific

August 29th, 2022 |

JMA Himawari-8 Visible (0.64 µm) images [click to play animated GIF | MP4]

2.5-minute rapid scan JMA Himawari-8 Visible (0.64 µm) images (above) showed rapidly-intensifying Category 4 Typhoon Hinnamnor as it moved across the West Pacific Ocean (southeast of Japan) on 29 August 2022. Mesovortices within the eye were faintly evident though breaks in patchy high clouds overhead.

2.5-minute Himawari-8 Infrared (10.4 µm) images (below) revealed a few pulses  of convection which exhibited cloud-top infrared brightness temperatures of -80°C and colder (violet pixels).

JMA Himawari-8 Infrared (10.4 µm) images [click to play animated GIF | MP4]

A DMSP-17 SSMIS Microwave (85 GHz) image at 2142 UTC from the CIMSS Tropical Cycones site (below) also depicted the well-defined eye and eyewall structure.

DMSP-17 SSMIS Microwave (85 GHz) image at 2142 UTC [click to enlarge]

===== 30 August Update =====

Himawari-8 Infrared (10.4 µm) images [click to play animated GIF | MP4]

On the following day, Himawari-8 Infrared (10.4 µm) images (above) showed the well-defined eye and surrounding eyewall as Hinnamnor reached Category 5 intensity at 1200 UTC. An eyewalll replacement cycle began around 2100 UTC, leading to a slight decline in intensity (to Category 4) and a deteriorating eye structure.

Post-sunrise Himawari-8 Visible (0.64 µm) images (below) better showed how close the eye passed to the Japanese islands of Kitadait?jima (RORK, where winds gusted to 98 knots) and Minamidait?jima (ROMD, where winds gusted to 69 knots).

JMA Himawari-8 Visible (0.64 µm) images [click to play animated GIF | MP4]

In a toggle between nighttime Suomi-NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images valid at 1717 UTC, viewed using RealEarth (below), the Day/Night Band image displayed a bright lightning streak just southwest of the eye — showing clouds within the eyewall being illuminated by intense lightning activity; cloud-top gravity waves were evident southeast of the eye in the Infrared image.

Suomi-NPP VIIRS Infrared Window (11.45 µm) and Day/Night Band (0.7 µm) images valid at 1717 UTC [click to enlarge]