During the day of 27 March 2026, a band of strong strorms propagated from north of the Samoan islands southward to the island themselves. These storm were notable for deep convection and strong environmental instability and were the cause of flood warnings across American Samoa.

A good first look at the environment supporting these storm comes from the NUCAPS vertical profile retrievals. Here’s a profile from the NOAA-20 satellite from just south of the area where convection formed. This is from 13:23 UTC, which corresponds to 2:23 AM in American Samoa Standard Time. Even though it’s the middle of the night, 4822 J/kg of surface-based CAPE is present. The downdraft CAPE is also significant at 895 J/kg, and the sounding is moist (although not atypically high for this region) at 1.87 inches of precipitable water. Together, these values indicate a strong possibility of deep convection and significant rainfall.

The CIMSS MIMIC-TWP2 brings some larger-scale context to the high amounts of water vapor. This loop spans from 0400 UTC on the 27th to 0500 UTC on the 28th. Looking at the Samoan Islands (southwest of the intersection of 10 S and 170 W), it’s clear that they lie in the heart of a strong plume of atmospheric moisture.

The Band 13 (10.3 micron) imagery from GOES-18 also helps show the intensity of the convection, with numerous overshooting tops seen throughout this field of view. These are seen as the grey regions embedded in the darker black areas in the enhanced color scale on the Band 13 imagrey.

It may be easier to recognize the areas of intense convection using the Day Convection RGB. Here, the most vigorous updrafts are visible as bright yellows. Note that the colors seem to fade to a more pastel tone as the loop continues. This is because this particular loop runs between 0100 to 0450 UTC on the 28th. That’s 2:00 to 5:50 PM in local time, and sunset is at 6:28 PM. This product depends on several different shortwave channels (0.64, 1.6, and 3.9 microns) and thus the fading daylight at the end of this loop makes this product increasingly unreliable.

An interesting phenomenon can be seen in the visible imagery during the morning. Lots of outflow boundaries are seen propagating southward of the main convection located to the north of the Samoan islands; note the thin bands of clouds that form in the middle of the image at the end of the loop. Here is where we are seeing the impact of the strong downdraft CAPE (DCAPE) from the NUCAPS sounding at the top of this post. DCAPE represents the tendency of a parcel that is perturbed downwards to keep going down. Areas with high DCAPE are prone to strong evaporatively-cooled downdrafts which force strong winds when they collide with the surface and propagate outward. These downbursts fizzled out before they reached land which makes it hard to determine just how strong they are given the lack of surface observations in the ocean.

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2.5-minute Target Sector JMA Himawari-9 AHI Infrared images (above) showed Cyclone Narelle after it had rapidly intensified to a 115 kt Category 4 storm (JTWC discussion | ADT | SATCON) off the coast of Western Australia on 26 March 2026. As Narelle moved southwestward toward the Exmouth Peninsula, it weakened slightly to a 110 kt Category 3 storm by 2100 UTC.  The coldest cloud-top infrared brightness temperatures were in the -90 to -95C range.

A plot of surface report data from Learmonth Airport (below) depicted a wind gust to 104 kts at 2200 UTC.

Himawari-9 Infrared images with an overlay of Deep-Layer Wind Shear (below) indicated that Narelle was moving through an environment of very low shear — which, along with warm Sea Surface Temperatures favored the intensification that Narelle experienced.

Microwave images from ATMS (above) and DMSP-18 (below) displayed signatures of a partial inner eyewall surrounded by a more complete outer eyewall (with evidence of a moat-like structure separating the two) — indicating that an eyewall replacement cycle was occurring, which in addition to increasing land interaction likely halted further intensification.

Wind shear and microwave imagery were sourced from the CIMSS Tropical Cyclones site.

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5-minute CONUS Sector GOES-19 (GOES-East) Microphysics RGB images with an overlay of Next Generation Fire System (NGFS) Fire Detection polygons (above) showed the thermal signature of a fire that resulted from an explosion at the Valero oil refinery in Port Arthur, Texas late in the day on 23 March 2026. The initial NGFS thermal signature occurred at 2326 UTC, and lasted nearly 10 hours until 0916 UTC (the maximum values of probed NGFS parameters occurred at 2336 UTC). Surface winds were light southerly in the vicinity of the fire.

True Color RGB images from the CSPP GeoSphere site (below) indicated that the resultant cloud was slowly spreading west-southwestward away from the refinery just before sunset (as a precaution, residents of the western parts of Port Arthur were instructed to shelter in place for about 12 hours). A subtle overshooting top was evident in the 2346 UTC image — with the entire cloud casting a shadow eastward across Sabine Lake.

A plot of rawinsonde data from nearby Lake Charles KLCH (below) indicated that the transition to northeast winds (that transported the bulk of the fire-generated cloud southwestward) occurred between the Lifting Condensation Level (at 852 hPa, or 1525 m) and the base of the strong subsidence inversion (at 825 hPa, or 1792 m).

As the fire continued to burn into the nighttime hours, a thermal signature (brighter pixels) was also apparent in GOES-19 Near-Infrared images (below).

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A persistent Kona low coupled with strong water vapor transport from an atmospheric river has brought devastating floods to the state of Hawaii in late March 2026. Rain totals over the past ten days have exceeded 40 inches in some locations, prompting evacuation orders for thousands. Over two hundred people have been rescued from the rising flood waters.

The CIMSS MIMIC-TPW2 product gives a good overview of the situation. Here’s it possible to see how the cyclone circulation northeast of Hawaii is drawing the moisture-laden water northward from the near-equatorial region. As that air reaches the Hawaiian archipelago, the orography of the islands contributes to vertical lifting and enhances the rainfall.

Synthetic Aperture Winds from the Sentinel-1 satellite on 21 March show the largely southerly flow running into the island of Maui, where the influence of the terrain on rainfall is going to be significant; similar effects are happening on the other islands.

The Japan Aerospace Exploration Agency (JAXA) Global Change Observing Mission (GCOM) satellite is one that is monitored by CIMSS’s and NOAA’s network of ground-based direct broadcast antennas. With an antenna in Honolulu, CIMSS is able to produce low-latency products from polar orbiting satellites, including from GCOM’s Advanced Microwave Scanning Radiometer (AMSR2). Here’s an animation of the 36.5 GHz microwave brightness temperature, which is sensitive to deep precipitation-producing clouds, from 15 to 21 March 2026. This and other direct broadcast products from Hawaii produced by CIMSS can be seen here. It’s clear that for every day for nearly a week, persistent strong rain has been present over Hawaii.

As of the morning of Sunday 22 March, the National Weather Service anticipates the low continuing to move off to the northeast with atmospheric flow over Hawaii returning to a more typical trade wind pattern. Due to the devastation wrought by this event, the islands and their people will take much longer to return to normal.

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