1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible images (above) included time-matched (+/- 3 minutes) plots of SPC Storm Reports — which showed the tornadoes, large hail (up to 4.00″ in diameter) and damaging winds (as high as 88 mph) that occurred across much of southern Wisconsin (along with adjacent parts of far northeast Iowa and far southeast Minnesota) on 14 April 2026. Numerous overshooting tops were seen in the Visible images.

The corresponding 1-minute GOES-19 Infrared images (below) revealed pronounced enhanced-V cloud-top signatures with several of the severe thunderstorms.

The coldest cloud-top infrared brightness temperatures exhibited by pulses of overshooting tops were -78ºC (brighter white pixels embedded within dark black areas) — which corresponded to a significant (~2 km) overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL), according to plots of rawinsonde data from Davenport, Iowa (below). CAPE values of 4000-4300 J/kg indicated that significant instability was present south of a frontal boundary which was draped across Iowa, Wisconsin and lower Michigan.

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2.5-minute Target Sector JMA Himawari-9 AHI Visible images (above) showed Super Typhoon Sinlaku as its eye approached Saipan (station identifier PGSN) in the Mariana Islands on 13-14 April 2026. Mesovrticies were evident within the eye. After reaching its peak intensity on 12 April (blog post 1 | blog  post 2), Sinlaku was in the process of a gradual weakening trend, decreasing from Category 5 intensity to Category 4 intensity by 0000 UTC on 14 April (JTWC discussion).

A longer animation of Himawari-9 Infrared images (below) showed Sinlaku making landfall on the islands of Saipan and Tinian, as a Category 4 storm around 1432 UTC on 14 April.

Microwave imagery (source) from ATMS (below) displayed the large outer eyewall ring that remained after Sinlaku had undergone a recent eyewall replacement cycle. The islands of Saipan and Tinian were located within this large eyewall.

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2.5-minute Target Sector JMA Himawari-9 AHI Infrared images (above) showed Super Typhoon Sinlaku as it rapidly intensified to a 160-knot Category 5 storm (ADT | SATCON) by 1800 UTC on 12 April 2026, southeast of Saipan (station identifier PGSN) in the Mariana Islands. Cloud-top infrared brightness temperatures began to gradually warm once Sinlaku reached peak intensity.

A nocturnal NOAA-20 VIIRS Day/Night Band image (below) provided a stunning example of mesospheric airglow waves that were propagating radially outward from Sinlaku.

Microwave images from DMSP-18 and ATMS (below) did display evidence of dry air becoming entrained into the circulation of Sinlaku, which was beginning to surround the well-defined eye and eyewall..

Sinlaku was moving through an environment characterized by fairly low values of deep-layer wind shear (below) — one factor which favored the rapid intensification of this tropical cyclone.

Sinlaku was also traversing warm water, as seen in relatively high values of Sea Surface Temperature and Ocean Heat Content (below).

Himawari-9 Infrared images with plots of Mesoscale Atmospheric Motion Vectors or AMVs (below) highlighted areas of high-altitude radial outflow — which enhanced upper-level divergence and promoted the maintenance of convective updrafts.

Microwave, Wind Shear, Sea Surface Temperature, Ocean Heat Content, Mesoscale AMVs, ADT and SATCON images/plots were sourced from the CIMSS Tropical Cyclones site.

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Typhoon Sinlaku (whom we introduced to you two days earlier when it was a mere tropical storm) has undergone steady and significant intensification and has now reached Category 5 status with estimated winds as high as 150 knots (170 mph). Satellite imagery of Sinlaku depicts it as a nearly perfectly symmetric eye with a tight and consistent circulation surrounding it. Here is the view from the Band 13 (10.4 micron) channel aboard Himawari-9, which provides the best geostationary view of the western Pacific Ocean.

The ATMS Band 18 (183 GHz) microwave imagery (courtesy of the CIMSS Tropical Cyclone page) shows a very similar story. Different microwave bands require different interpretations, but here the interpretation is relatively straightforward: the cold brightness temperatures of the eyewall and precipitation bands are easily contrasted against the warmth of the uniform ocean background.

By contrast, ATMS channel 8 (55 GHz) shows the warm temperature anomaly that is at the heart of a warm-core low like a strong tropical system. Since tropical cyclones are latent heat machines, their center is warmer than the surrounding areas. This is one trait that sets them apart from the baroclinic midlatitude systems that may look similar but have drastically different characteristics, including a cold central core.

The CIMSS Deep Multispectral INtensity of TCs estimator (D-MINT) automated estimation of cyclone intensity has been tracking this storm from the beginning, showing its steady increase from an invest all the way to a Category 5 storm. The Joint Typhoon Warning Center cites these values in estimating Sinlaku’s wind speed as part of its prognostic reasoning.

Recent forecasts have been pushing the track slightly northward and projecting a path over Saipan. Tropical storm conditions are still expected for Guam. One good note in the evolution of this system is that the Air Mass RGB seems to indicate that Sinlaku is moving into a region of drier day, which it may soon start ingesting and which could contribute to its weakening in the future. This dry air is discernible as the areas of orangish-brown against the greener colors of the more moist air.

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