10-minute Full Disk scan GOES-18 (GOES-West) Infrared Window images (above) showed Hurricane Nolo as it was intensifying from a Category 1 to a Category 2 storm while approaching the International Dateline (180 degrees longitude) on 04 October 2026. Once the tropical cyclone crossed the International Dateline, its ocean-basin-specific designation changed from Hurricane Nolo to Typhoon Nolo. The diameter of Nolo’s eye increased as it approached the Dateline — and the coldest cloud-top infrared brightness temperatures associated with deep convection were around -77C.

An overlay of GOES-18 GLM Flash Extent Density (below) revealed intermittent lightning activity with Nolo — which was less frequent within the eyewall region.

Illumination from the Moon (in its Waning Crescent phase, at 37% of Full) provided a nighttime visible image of compact Hurricane Nolo using the VIIRS Day/Night Band on NOAA-20 (below).

A Synthetic Aperture Radar (SAR) image from Canada’s RCM-2 satellite (below) sensed surface wind speeds as high as 121.35 knots in the NW quadrant of Hurricane Nolo.

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It’s time to grab an apple cider donut and a pumpkin spice latte if you’re in the upper Midwest, because fall has arrived in the northern regions of the central United States. In the upper peninsula of Michigan, freeze warnings are out, and while other parts of the Midwest might not be quite so cold just yet, there is a definite nip in the air that wasn’t there a few weeks ago.

Of course, one of the most beloved characteristics of this seasonal transition is the change in the leaf colors. And what better way to track that then by satellite? Here’s an animation of the past two weeks of GOES-19 (GOES East) true color views courtesy of CSPP Geosphere. This animation shows a snapshot of the true color product at 1600 UTC (noon EDT, 11:00 AM CDT) so the solar illumination is roughly the same from one frame to the next. Watch how the tree colors in the upper midwest change from green to a rusty copper instead, at least when there aren’t any clouds in the way.

Something important to remember, however, is that the GOES true color view isn’t really a true color. Our eyes are sensitive to red, green, and blue. The GOES Advanced Baseline Imager (ABI) has a red channel and a blue channel, but it doesn’t have a green channel. Instead, this product uses a channel that is sensitive to vegetation and shades that as green in this RGB product. Basically, ABI can’t see green, but it knows what a lot of the green things look like in the near infrared, and so we pretend that when we see those things using a near IR channel, we can act as those things are actually green.

But other satellite imagers have a “true” true color product. VIIRS, for example, has a legitimate green channel. Let’s compare VIIRS to GOES ABI for the same scene and see how the two compare in their color rendition. Check out the slider below, in which GOES is on the left and VIIRS is on the right. Note how the GOES view just has an overall more greenish cast than the VIRS view does. For much of the year, the great plains are covered in green vegetation and so that green color is good enough. But as the vegetation transitions into the autumn season, its colors change in a way that the GOES true color RGB wasn’t designed for.

So let’s take a look at the VIIRS observations in closer detail. Here’s another slider, this time showing the difference in the VIIRS true color product between 23 September and 2 October 2026. The change between the two is astonishing. It’s no wonder why fall tourism is such an important part of year in this part of the United States.

Frequent readers of the CIMSS Satellite Blog know that satellites are good for more than just pretty pictures, however. We can actually get useful quantitative values from these observations. The EU Copernicus Browser enables users to interact with the Sentinel series of satellites, including plotting time series of observations. The Sentinel-2 satellite has 13 bands, including true red, green, and blue channels. Here, we’ve implemented a normalized red/green index: [(G – R) / (G + R)]. This looks at the difference between the red and green channels and divides that by the sum of the two so that the values are always limited to be between –1 and 1. During the summer months, the red reflectance is relatively small compared to the green reflectance, so the values will be positive. As the season transitions to fall, however, the green tends to go away and redder colors start to dominate. As a result, this normalized channel difference will trend to negative numbers as the seasons shift and the leaves change their color. That’s exactly what we see happening over the last week of Sentinel observations over the Keweenaw Peninsula in Michigan’s Upper Peninsula. Look at the steady downward trend starting around September 22.

The CIMSS Satellite Blog encourages you to get outside and enjoy one of the best times of the year.

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1-minute Mesoscale Domain Sector GOES-18 (GOES-West) Infrared Window images (above) displayed the cold cloud tops and periodic consolidation of a small and well-defined eye associated with Hurricane Rachel as it reached Category 3 intensity over the East Pacific Ocean (about 200 miles west of Mexico) on 01 October 2026. GLM Flash Points highlighted the intermittent lightning activity within deep convection surrounding the eye. The coldest cloud-top infrared brightness temperatures were around -90 C (darker shades of purple).

In the corresponding 1-minute GOES-18 Visible images (below), the eye became mostly cloud-cleared for a few very brief periods.

Products from the CIMSS Tropical Cyclones site showed that Rachel was moving through an environment of low shear and traversing warm water (Sea Surface Temperature | Ocean Heat Content) — factors which favored its intensification.

Plots of ADT and AiDT (automated methods which objectively estimate tropical cyclone intensity using geostationary infrared imagery) depicted the brief period of Rachel’s more rapid intensification that began around 1800 UTC on 01 October (below).

After sunset, ample illumination from the Moon (in its Waning Gibbous phase, at 60% of Full) provided nighttime visible images of Rachel via the VIIRS Day/Night Band on Suomi-NPP and NOAA-20 (below).

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2026 continues to be an intense year for hurricanes in the eastern Pacific Ocean as Nolo became the 6th system in that basin to reach category 4 or greater during this year. Its ascent to major hurricane status was also quite fast; over the course of less than 24 hours on the 26th and 27th of September 2026, Nolo strengthened from a strong Category 1 storm all the way to the Category 4/Category 5 boundary as it propagated westward to the south of Hawaii. Let’s take a look at 24 hours of hourly geostationary Band 13 images from GOES-18 (GOES West) showing the intensification of the storm. Watch how the eye transitions from somewhat irregularly-shaped to a perfect circle at the same time the cloud top temperatures drop significantly.

One of the GOES-18 mesoscale sectors was trained on Nolo as it underwent its intensification. Here’s the one-minute mesoscale imagery from 1300-1300 UTC (3:00–3:30 AM local time). You can even see what appears to be gravity waves propagating outward along Nolo’s top, especially in the northeastern sector of the storm, which would be indicative of very strong updrafts.

The CIMSS Tropical Cyclone group, as always, has been monitoring Nolo with a suite of products. Here’s a time series of the D-MINT automated intensity estimates. According to D-MINT, Nolo briefly peaked at Category 5 before rapidly declining. D-MINT also gives us an appreciation of how long Nolo hung around as a tropical depression before it began its intensification.

The CIMSS MIMIC product is sued to provide microwave imagery from polar orbiting satellites at geostationary-like time intervals. Here is an animation from 0000 on the 27th to 0000 on the 28th (2:00 PM on the 26th to 2:00 PM on the 27th), depicting the consolidation of a strong eye wall around the center of rotation.

So what caused this rapid intensification? The the weekly sea surface anomaly plot from NOAA’s Physical Science Laboratory can provide some insight. Note how the waters south of Hawaii are 1-2 degrees above normal while this year’s El Niño rages along the Equator.

The high winds are captured by satellite observations as well. Here’s a view of the synthetic aperture radar (SAR)-derived wind speed from one of Canada’s RADARSAT polar-orbiting satellites. Remember, SAR can only detect wind speed, not wind direction, so the directional indicators in this image are from numerical weather output. This particular image is from 1634 UTC (6:34 AM local time) on the 27th, when the storm was undergoing its intensification. Observed winds in teh northwestern sector are clearly exceeding the 100 kt top end of the color scale.

Nolo did have some impacts on the southern coasts of some of the Hawaiian islands, including flash flooding, tropical-storm-level wind gusts, and heavy surf. It is anticipated that Nolo will continue to weaken as it moves into the cooler waters west and northwest of the state of Hawaii.

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