Today is the Fall Equinox in the northern hemisphere and a great opportunity to show off some full disk GOES images. The passing of the seasons has always been marked by humans, sometimes because of agricultural significance, spiritual significance, community bonding, or simply to mark time. The fall (or autumnal) equinox marks the time when the sun is directly above the equator, as we transition seasons from summer to fall in the northern hemisphere (and it’s going from spring to summer in the southern hemisphere). This year the fall equinox is September 22, 2026. It can be seen in GOES visible band imagery at satellite sunrise or sunset where the terminator (the dividing line between night and day) is aligned perfectly north/south in the middle of a full disk visible band image. For the people in the northern hemisphere, the autumnal equinox marks the end of summer and the beginning of autumn, which lasts until the winter solstice (usually December 21). This is the astronomical definition of the changing of seasons as the tilt of the earth on its axis will lead to summer in the southern hemisphere as we head into winter up here in the northern hemisphere.

Sunset and sunrise time-lapse animations from space (below) show the progression of the terminator from spring equinox, through summer solstice, to fall equinox from the satellite’s point of view. For these times of day the disk is “half” illuminated so the terminator formed by the shadow of the night-side of earth is easy to track. GOES-East sits over the equator above 75 West (which is in Columbia, near where the borders of Peru, Ecuador, and Columbia meet) and GOES-West sits over the equator above 137 West (which is out in the Pacific Ocean away from any major land masses – maybe the closest thing is French Polynesia, 680 miles to the southwest; and for reference, Hawaii is over 1700 miles to the northwest of the GOES-West subpoint). These two views provide coverage of nearly two thirds of the earth and so in addition to the terminator you can see some of the things that affected life across our hemisphere from major storm systems to smoke and dust. Technically sunrise, sunset, and local noon vary from day to day, but these animations use a consistent time every day that is close to sunrise or sunset.

Looking back at the past 6 months or so the CIMSS Satellite Blog has been full of interesting cases. We’ve covered: Earth Day, fog, flooding, hail, thunderstorms, tornadoes, tropical storms, volcanic eruptions, wildfires and more!

View only this post Read Less

Overlapping 1-minute Mesoscale Domain Sectors provided 30-second GOES-18 (GOES-West) Infrared Window images of Hurricane Polo (above) as it rapidly intensified from a Category 1 to a high-end Category 3 storm late in the day on 21 September 2026. An eye became apparent by the end of the animation (the overlapping Mesoscale Sectors ended at 0438 UTC on 22 September, when Sector 1 was re-positioned over the Southwest US).

Following the period of 30-second imagery, a single GOES-18 Mesoscale Sector provided 1-minute Infrared Window imagery for the remainder of the day on 22 September (below), as Polo continued to rapidly intensify to a Category 4 (at 0600 UTC) and then to a Category 5 hurricane (at 1200 UTC). It is interesting to note that as Polo was progressing toward its maximum intensity (at 1900 UTC), an Enveloped Eyewall Lighting Signature was evident in the concentration of GLM Flash Points (for example, at 1445 UTC or at 1637 UTC); however, this eyewall lightning then abruptly ended after about 1900 UTC. (The ~2 hour GOES-18 data outage and subsequent image degradation/striping was due to a NOAA firewall maintenance issue.)

In terms of central pressure — with a minimum of 892 hPa (SATCON) — Polo became the second-most intense hurricane on record in the East Pacific.

Within an hour of Polo reaching Category 5 intensity at 1200 UTC, a Synthetic Aperture Radar (SAR) image (below) from Canada’s RCM-3 satellite (source) depicted wind speeds as high as 144.37 knots in the NW quadrant of the hurricane.

Products from the CIMSS Tropical Cyclones site showed two factors that were favorable for Polo’s rapid intensification on 22 September: (1) moving through an environment of low to moderate vertical wind shear (0900 UTC | 1800 UTC), and (2) traversing warm water (Sea Surface Temperature | Ocean Heat Content).

View only this post Read Less

10-minute Full Disk scan GOES-19 (GOES-East) Infrared Window images (above) showed the evolution of Tropical Storm Fay in the East Atlantic Ocean on 20 September 2026. As of 0300 UTC on 21 September — the last image of the animation — NHC rated Fay’s wind speed at 60 knots (just 4 knots below Category 1 Hurricane intensity). GLM Flash Points indicated the presence of intermittent lightning activity within areas of deep convection.

A 2238 UTC overpass of Metop-C provided a swath of ASCAT winds – which had velocities as high as 53 knots (below).

Fay was becoming embedded within an environment of unfavorably-high northwesterly deep-layer wind shear, as shown below (sourced from the CIMSS Tropical Cyclones site).

As a result of increasingly-unfavorable wind shear, the low-level circulation center eventually became exposed as it was displaced to the west and northwest of Fay’s deep convection (below).

View only this post Read Less

The GOES-18 (GOES West) Advanced Baseline Imager showed something interesting off of California’s Cape Mendocino on the morning of Saturday, 19 September 2026. This cape is the westernmost point in California and is characterized by significant terrain changes over a relatively short distance. The Pacific Ocean next to the coast of California is frequently covered in stratocumulus clouds due to the relatively cold sea surface temperatures caused by the California current and its associated upwelling. These cold temperatures are clearly visible in the NOAA Sea Surface Temperature maps derived from satellite observations. Here’s the map for the previous day, 18 September 2026; note how the temperatures around Cape Mendocino (the westward-poking nub near the intersection of 40 N and 124 W) are around 13 C or 55 F.

These cold sea surface temperatures cause the air above the ocean to also become quite cold, cooling to the dew point and forcing the formation of clouds. Since air is a poor conductor of heat, the air further away from the surface does not cool which causes a notable inversion to form and which limits the vertical extent of the clouds that develop. This can result in quite widespread deck of these clouds over cool ocean regions, as can be seen in this geocolor RGB image from GOES-18. Note how, outside of some valley fog, California is basically cloud-free while the ocean immediately adjacent is overcast with marine stratocumulus.

But there’s an exception to this idea that the entire west coast is socked in with clouds. Let’s zoom in on the area around Cape Mendocino with this animated true color loop. While it’s always fun to watch valley fog dissipate with the rising sun, here pay special attention to what’s happening south of the cape.

The winds are predominately northerly and it’s easy to see how the clouds are streaming southward because of that. But in the wake of the Cape, the skies are clear over the ocean. What’s going on here? To get a better idea, let’s take a look at the terrain of Cape Mendocino, courtesy of the US Geological Survey National Map. Here, there’s a topographic map with a transect drawn across the cape to give an idea of the terrain.

As you can see, over a short distance the terrain goes from the ocean at sea level to peaks near 3,000 feet. That’s quite a jump over a relatively short distance and the southerly flow is forced to deflect around the cape. In the wake of the northerly flow that is blocked by the terrain of the cape, drier continental air (enhanced by downsloping) is able to enter that region and prevent clouds from forming despite the quite cold sea surface temperatures. There even seems to be a hint of a terrain-forced mesolow with some southerly flow appearing right next to the coast in this region.

Note how difficult it is to see this clear spot in the infrared imagery, however. This is because the clouds are so shallow that there is very little difference between their temperature and the temperature of the ocean. Because we know what we’re looking for, we can probably identify the clearing region, but we’d likely have to resort to some other product to help discern between clear sky and cloud cover for a region that we hadn’t already been looking at.

View only this post Read Less