Target Sector (2.5-minute interval) JMA Himawari-9 AHI Clean Infrared Window (10.4 µm) images (above) showed the gradual development of a ragged eye with Cyclone Jasper as the storm moved southward across the Coral Sea on 07 December 2023. Intermittent convective bursts within the eyewall contained a few overshooting tops that exhibited infrared brightness temperatures around -90ºC (yellow pixels embedded within dark purple areas).

The partially-fragmented structure of the eyewall was evident in a DMSP-17 SSMIS Microwave image at 0816 UTC (source) (above) and a RCM-1 Synthetic Aperture Radar wind speed image at 0807 UTC (source) (below).

Himawari-9 Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Jasper was moving through an environment of low deep-layer wind shear — which, in addition to its motion across warm water (SST | OHC) favored continued intensification.

Jasper was upgraded to Category 3 intensity at 1800 UTC (JTWC discussion) — and a DMSP-17 SSMIS Microwave image at 1927 UTC (above) as well as a RCM-3 SAR wind speed image at 1914 UTC (below) displayed a more organized eyewall structure.

Jasper was subsequently upgraded to a Category 4 storm at 0000 UTC on 08 December (SATCON), as the satellite presentation of the eye improved in Himawari-9 Infrared images — and mesovortices within the eye were revealed in Visible images (below).

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A sequence of 5-minute CONUS Sector GOES-18 (GOES-West) Lower-level Water Vapor (7.3 µm), Mid-level Water Vapor (6.9 µm), and Upper-level Water Vapor (6.2 µm) images (above) revealed the diurnal cycle of nighttime cooling and daytime warming at the summits of Mauna Kea and Mauna Loa on the Big Island of Hawai’i on 06 December 2023. This case is another example which helps to underscore the fact that Water Vapor spectral bands are essentially Infrared bands, which — in the absence of clouds, and in a dry atmosphere — can sometimes sense surface features.

The presence of very dry air within most of the middle/upper troposphere over Hawai’i on 06 December had the effect of shifting the water vapor weighting functions to lower altitudes, as seen on plots for the 3 ABI Water Vapor spectral  bands calculated using rawinsonde data from Hilo PHTO (below). This allowed thermal radiation from the higher terrain of Mauna Kea and Mauna Loa to pass upward — with minimal attenuation — through what little high-altitude moisture was present, and reach the 7.3 µm / 6.9 µm / 6.2 µm detectors on the GOES-18 ABI instrument. The 2 mountain summits extend upward to near the 600 hPa pressure level — close to the level of peak weighting function contributions for Water Vapor spectral bands 09 and 10 — and to an altitude where there was still a contribution from the Band 08 weighting function, as calculated using the Hilo soundings.

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Hourly GOES-18 Hemispheric views, above, from 2140 UTC on 1 December to 2040 UTC on 4 December, (from the CSPP Geosphere site) show the development of a strong system in the Gulf of Alaska. This system is tapping into an airstream rich in moisture that augurs for a wet period along the Pacific Northwest coast. Flood watches and have been issued from western Washington and Oregon. MIMIC Total Precipitable Water fields in December ending at 1500 UTC on 4 December, below, show that some of the moisture in the North Pacific may have been part of the Kona Low that drenched Hawai’i last week.

Airmass RGB imagery from GOES-18, below (from this OSPO site), shows the well-developed cyclone with the characteristic orange signal in the airmass RGB denoting air with a large Potential Vorticity signal (as confirmed in this cross-section from1800 UTC on 4 December, take from this site).

For more information on this event, refer to the websites of the National Weather Service Offices in Seattle, Portand and Medford.

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Tropical Cyclone Michuang has formed in the Indian Ocean. Michuang, which means strength or resilience, is situated in the Bay of Bengal on 2023-12-04. Michuang’s center is currently about 48 km from the east coast of the Indian subcontinent. But the bands of the system have already caused major storm surges in the states of Andhra Pradesh and Tamil Nadu. In cities such as Chennai, India, schools are closing and air travel has been put on a pause. Two fatalities are associated with the flooding and high winds. Thousands have been asked to evacuate. The storm is forecast to make landfall on 2023-12-05 at approximately 12Z and may arrive with gusts as high as 68 miles per hour.

RealEarth provides a global infrared product that has full-earth coverage. Watch an animation of infrared data as Tropical Cyclone Michuang develops over the past 48 hours. At infrared wavelengths, users can watch the system develop and organize into its cyclonic structure.  

Another product that can be used to investigate the moisture in Tropical Cyclone Michuang is the MIMIC Total Preciptable Water product (MIMIC-TPW). MIMIC-TPW uses several sensors operating at microwave frequencies to estimate the total precipitable water field. Taking a look at the product below, Michuang is associated with a large area of high TPW values. It is no surprise that this storm is causing major rains and flooding.

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