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 by 1800 UTC (ADT | SATCON) southeast of Saipan (station identifier PGSN) in the Mariana Islands on 12 April 2026. 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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As the Artemis II mission (which launched on 01 April) was coming to its successful end late in the day on 10 April 2026, the Orion crew module “Integrity” approached the designated landing site off the coast of San Diego, California. The Orion module generated immense heat (up to 5000°F or 2760°C) and a very bright glow as it was re-entering the Earth’s upper atmosphere — and at the point of peak heating (which occurred at an altitude around 204000 ft or 62 km) the GOES-18 (GOES-West) GLM instrument interpreted that bright re-entry signature as a southwest-to-northeast oriented streak of lightning at 2355 UTC (above).

A larger-scale image (below) showed that the GOES-18 GLM signature was located over the East Pacific Ocean about midway between Hawai`i and southern California.

A toggle between GOES-18 Infrared, Visible and Visible + GLM Flash Extent Density / Flash Point images (below) showed that there was no deep convection in that area — so the GLM signatures were not associated with any meteorological features.

The GOES-18 GLM Flash Point with the longest duration and largest flash area was located along the leading (northeast) portion of the signature (below).

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A somewhat unusual event could be found on the morning of 10 April 2026 when twin tropical cyclones could be found in the western Pacific. Since each storm was on the other side of the equator, the two systems were rotating in opposite directions. To the north was Sinlaku, a developing storm that is projected to intensify into typhoon strength with the potential to bring adverse impacts to Guam on Monday the 13th. To the south is Maila, a storm that is weakening from its peak strength and which was featured in the Blog earlier this week. Here is an animation of both storms from the Himawari-9 True Color product; remember, unlike the GOES series the Advanced Himawari Imager has a true green channel in addition to its red and blue channels, making for a product that looks slightly different when compared to the American satellites (which assume that a channel that has strong vegetation reflectance is a reasonable proxy for green).

NOAA’s satellite-derived seat surface temperatures, courtesy of the Office of Satellite and Product Operations, show sea surface temperatures around 29 C (84 F) for both systems. However, Maila is in a region of stronger shear and moving toward a region of colder sea surface temperatures, and so it is expected to continue to weaken. Here is an inset of the SST map showing the warm waters around the equator.

While the storms look similar on the visible wavelength imagery, Maila and Sinlaku look rather different on the AHI Band 13 (infrared window) satellite loop. This product shows warmer cloud tops for the southern storm, indicative of weaker convection.

However, that weather convection does not necessarily translate to weaker winds. Here is a mosaic of winds observed by the OSCAT-3 scatterometer. Note how Maila still has plenty of winds greater than 50 knots encircling a tight center of rotation. While this storm is weakening, as of this set of images it is still a Category 1 cyclone and still has the potential for negative impacts to the eastern islands of Papua New Guinea.

The CIMSS MIMIC-TPW2 product also show the twinned nature of these two systems, with clear signals of cyclonic, but mirrored, rotation on either side of the Equator. Note the extreme levels of total precipitable water just to the west of New Guinea on the left side of the animation. Also evident at around 30 S are the remains of Vaianu, a former category 3 tropical cyclone that now shows clear signs of extratropcial evolution.

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