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Flooding on Maui and Oahu

Infrared imagery over the Hawai’ian Islands on 25/26 October, below, shows convective development over Maui and Oahu. This was also a region of strong vertical wind shear, as shown below, as upper level cloud features were moving southeastward, low level clouds were moving to the west).GREMLIN is a machine-learning tool... Read More

GOES-18 Band 13 (Clean Window infrared, 10.3 µm) imagery, 1411 UTC 25 October through 0001 UTC 26 October 2024 (Click to enlarge)

Infrared imagery over the Hawai’ian Islands on 25/26 October, below, shows convective development over Maui and Oahu. This was also a region of strong vertical wind shear, as shown below, as upper level cloud features were moving southeastward, low level clouds were moving to the west).

850-200 mb wind shear, 1800 UTC on 26 October 2024 (Click to enlarge)

GREMLIN is a machine-learning tool that uses Bands 7, 9 and 13 fields from GOES-18 to emulate what NEXRAD radar echoes might look like. The animation below shows GOES-18 infrared data, and GREMLIN radar estimates. GREMLIN shows radar returns over both Oahu and Maui.

GOES-18 Band 13 (Clean Window infrared, 10.3 µm) imagery (left) and GREMLIN Radar Emulation (dBz, right), 1411 UTC 25 October through 0001 UTC 26 October 2024 (Click to enlarge)

Strong convection with radar returns occur over both Maui and Oahu after 1500 UTC. The National Weather Service in Honolulu issued Flash Flood Warnings at 1638 UTC for Maui and at 1640 UTC for Oahu. The side-by-side animation, from 1501-1701 UTC shows the heavy rain indicated by GREMLIN as the Flash Flood Warning was issued.

GOES-18 Band 13 (Clean Window infrared, 10.3 µm) imagery (left) and GREMLIN Radar Emulation (dBz, right), 1501-1701 UTC 25 October 2024 (Click to enlarge)

The Hilo sounding from 1200 UTC on 26 October, below, (from here) shows a moist atmosphere (55 mm of Total Precipitable Water) and mid-level instability. MIMIC Total Precipitable Water (TPW) at that time (here) shows the horizontal distribution of the moisture.

Upper-air sounding at Hilo HI (91285) at 1200 UTC on 26 October 2024 (Click to enlarge)

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Strong winds south of a low pressure system in the Beaufort Sea

A sequence of Suomi-NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (above) showed the cyclonic swirl of clouds associated with a low pressure system that was moving eastward across the Beaufort Sea on 25 October 2024. The relatively tight pressure gradient south of this low (surface analysis)... Read More

Sequence of Suomi-NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images, with an overlay of METAR site surface winds (white) and Peak Wind gusts (cyan/red) on 25 October [click to play MP4 animaton]

A sequence of Suomi-NPP VIIRS Day/Night Band (0.7 µm) and Infrared Window (11.45 µm) images (above) showed the cyclonic swirl of clouds associated with a low pressure system that was moving eastward across the Beaufort Sea on 25 October 2024. The relatively tight pressure gradient south of this low (surface analysis) was forcing fairly strong W-SW winds across the North Slope and Arctic coast of Alaska (as well as the adjacent Canadian provinces of Yukon and the Northwest Territories).

A Suomi-NPP VIIRS Day/Night Band image with an overlay of Metop-B ASCAT winds (below) depicted the flow across the offshore waters north of Alaska — where Heavy Freezing Spray Warnings were issued for the ice-free waters. Numerous ASCAT wind speeds were in the 30-35 knot range.

Suomi-NPP VIIRS Day/Night Band (0.7 µm) image, with an overlay of METAR site surface winds (white) and Peak Wind gusts (cyan/red) and Metop-B ASCAT winds (green) [click to enlarge]

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Potential tropical cyclone formation near Guam

The Joint Typhoon Warning Center is currently monitoring two areas of interest of near Guam for potential tropical cyclone formation. The first, 99W, is located due east of Guam, while the second invest, 98W, is further southeast. During the local overnight hours today between 14:54 and 16:11 UTC, the VIIRS instruments onboard S-NPP,... Read More

The Joint Typhoon Warning Center is currently monitoring two areas of interest of near Guam for potential tropical cyclone formation. The first, 99W, is located due east of Guam, while the second invest, 98W, is further southeast. During the local overnight hours today between 14:54 and 16:11 UTC, the VIIRS instruments onboard S-NPP, NOAA-20, and NOAA-21 captured the following sequence of day-night band imagery:

Loop of VIIRS Day Night Band imagery centered over Guam between 14:54 and 16:11 UTC on October 24, 2024.

Overall, it is clear that the situation is a bit messy. In the DNB imagery, it is easy to pick out a few features of note, including a broad region of convection on the northern side of invest 99W, a narrow stripe of convection extending to the south all the way to invest 98W, and some hints of the low level circulation of 98W. This final feature highlights a case where DNB imagery can be very helpful in conjunction with geostationary IR imagery during the overnight hours.

Of course, some other polar satellite instruments can help diagnose the state of these circulations a bit further. For example, the 183 GHz band from ATMS is sensitive to water vapor, and that band’s imagery (processed via CSPP MiRS) from the NOAA-20 pass at 15:20 UTC is below:

ATMS / MiRS 183 GHz BT image centered over Guam from NOAA-20 at 15:20 UTC on October 24, 2024.

Over Guam and points west, there is a rather pronounced “tongue” of drier air. With invest 99W moving across the edge of this gradient, it will likely struggle to gain symmetry to its structure on its west side. Additionally, a key forecast challenge for invest 98W mentioned in the latest Area Forecast Discussion from NWS Guam is uncertainly regarding how this drier air mass will be influenced by the passage of 99W.

And finally, the AMRS2 instrument aboard GCOM-W1 offers a look inside the clouds of invest 99W at 89 GHz just a bit later at 16:05 UTC. This data confirms that no clear organization of the precipitation bands has taken place at this point.

AMSR2 89.0 GHz BT image centered over Guam from GCOM-W1 at 16:05 UTC on October 24, 2024.

All imagery in this post was collected by the SSEC direct broadcast antenna system located at NWS Guam. Those with interests in the western Pacific should stay tuned to local authorities for the latest updates. Thank you to Scott Lindstrom for guiding me through the process of writing my first post on the CIMSS Satellite Blog!

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Hurricane Kristy reaches Category 5 intensity

1-minute Mesoscale Domain Sector GOES-18 (GOES-West) Visible and Infrared imagery of Hurricane Kristy in the East Pacific Ocean on 23 October (above) highlighted a well-defined eye, with GLM-indicated lightning activity increasing within the inner eyewall. Cloud-top infrared brightness temperatures in the -80s C (shades of violet to purple) were apparent at times.... Read More

1-minute GOES-18 Red Visible (0.64 µm, left) and Clean Infrared Window (10.3 µm, right) images with an overlay of GLM Flash Points, from 1331-1600 UTC on 23 October [click to play MP4 animation]

1-minute Mesoscale Domain Sector GOES-18 (GOES-West) Visible and Infrared imagery of Hurricane Kristy in the East Pacific Ocean on 23 October (above) highlighted a well-defined eye, with GLM-indicated lightning activity increasing within the inner eyewall. Cloud-top infrared brightness temperatures in the -80s C (shades of violet to purple) were apparent at times. Kristy reached Category 4 intensity as of the 2100 UTC advisory from NHC.

A closer view of GOES-18 Visible images (below) revealed low-altitude mesovortices within the eye.

1-minute GOES-18 Red Visible (0.64 µm) images with an overlay of GLM Flash Points, from 1601-2100 UTC on 23 October [click to play MP4 animation]

Hurricane Kristy was moving through an environment characterized by low values of deep-layer wind shear, as seen in an analysis from the CIMSS Tropical Cyclones site (below) — a factor which favored its rapid intensification.

GOES-18 Infrared images, with an overlay of 2000 UTC deep-layer wind shear contours and streamlines

===== 24 October Update =====

1-minute GOES-18 Red Visible (0.64 µm, left) and Clean Infrared Window (10.3 µm, right) images with an overlay of GLM Flash Points, from 1802-2300 UTC on 24 October [click to play MP4 animation]

On 24 October, 1-minute GOES-18 Visible and Infrared imagery (above) again displayed a well-defined eye, with GLM-indicated lightning activity increasing within the inner eyewall — and cloud-top infrared brightness temperatures in the -80s C (shades of violet to purple) were apparent at times. Kristy continued to further intensify, becoming a Category 5 hurricane as of the 2100 UTC advisory from NHC.

In a closer view of GOES-18 Visible images (below), distinct low-altitude mesovortices were once again seen within the eye.

1-minute GOES-18 Red Visible (0.64 µm) images with an overlay of GLM Flash Points, from 1802-2300 UTC on 24 October [click to play MP4 animation]

Earlier in the morning, when Kristy was still a Category 4 hurricane, a Synthetic Aperture Radar (SAR) image at 1401 UTC (below) indicated that a derived maximum wind speed of 130 knots was present in the NE quadrant of the eyewall (source).

RCM-3 SAR image at 1401 UTC on 24 October [click to enlarge]

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