This blog author loves posting about the seasons! They provide the opportunity to post some awesome full disk GOES images, but there’s more than that. 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, 2025. 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 (around December 21 or 22). 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, sunset, or noon.

In this GOES-19 (GOES-East) animation in addition to seeing the terminator progress from equinox to summer solstice and back to equinox, there are multiple tropical storms visible, including Hurricane Erin in mid-August and Hurricane Gabrielle in the last few frames. One can also observe dust blowing off the African continent and the reflection of the sun migrating north from the equator and then back south to the equator.

In this GOES-18 (GOES-West) animation there are also multiple tropical storms visible. There have been 8 tropical storms and 8 hurricanes this year so far in the east Pacific, some of which caused major flooding in parts of Mexico. There was also plenty of wildfire smoke mixed in with the clouds over Canada and the northern half of the US during summer 2025, affecting air quality across wide areas of both countries.

In this GOES-18 (GOES-West) animation of local noon the seasonal transitions may be more difficult to spot. As the northern hemisphere transitions from spring equinox, through summer, to fall equinox, the earth’s tilt puts the southern hemisphere away from the sun. This can be seen at the bottom of these images at the south pole as it gradually gets darker and darker until the solstice (June 21) and then starts to get light again. That’s winter in Antarctica and there are days where it just stays dark all day for those scientists and support staff that work down there through their winter. Some of the tropical storms and hurricanes may be easier to watch in this animation as the whole disk is as well-illuminated as it gets at satellite noon.

This GOES-19 (GOES-East) animation is similar to the previous one, but now at sunset for the satellite (23:00 UTC).

View only this post Read Less

For the past few days, the eyes of the Philippines and Taiwan have been focused on a developing tropical system in the western Pacific. What began as a small group of convective cells northwest of Micronesia on 16 September 2025 has grown into the most intense tropical system up to this point in 2025. Super Typhoon Ragasa (called Nando in the Philippines as the Philippine national meteorological service maintains a separate list of typhoon names). A super typhoon is broadly equivalent to a strong category 4 hurricane on the Saffir-Simpson scale. For a storm to achieve super typhoon status, winds have to be in excess of 130 kts (the upper bound for a category 4 storm is 136 kts).

The rapid intensification of Ragasa can be seen in the Advanced Himawari Imager (AHI) view over the last three days starting at 0300 UTC in 19 September 2025. Using the Band 13 infrared view enables the consistent monitoring of the storm at all hours of the day.

We’ll discuss a few key moments from this loop. At the start of the animation (0300 UTC on 19 September), the system had just been classified as a tropical storm only a few hours earlier. Overall organization is weak and no eye is present.

However, this area was well-suited for tropical intensification. First, note the CIMSS MIMIC-2 total precipitable water (TPW) imagery from the same time as the above IR satellite view. TPW values are elevated in the western Pacific. Even outside of the storm itself (seen as the fuchsia area exceeding the top of the color scale), MIMIC indicates TPW of more than 60 mm west of the Philippines.

Second, the sea surface temperatures (SSTs)in this area were quite warm. The NCEP SST product, as mapped by SSEC, shows temperatures approaching 32 C (90 F).

In fact, these temperatures are 1-2 C above normal, as determined by the NOAA Coral Reef Watch daily SST anomaly plot, seen here for 19 September.

With lots of atmospheric moisture and significant amounts of warm oceanic water, the latent heat machine that drives tropical systems sprang into life, and the newly christened Ragasa quickly intensified. By 2100 UTC on the 19th, an eyelike structure could be seen at the center of rotation.

Over the next day, the eye structure strengthened and then went through an eyewall replacement cycle but retained its strength at teh conclusion of that process. Evacuations were ordered for parts of the Philippines and Taiwan in anticipation of landfall. Sustained winds in excess of 115 kts were reported at 0000UTC on the 21st as the storm exhibited a compact eye.

By 0000 UTC on the 22nd, those sustained winds had increased to 145 kts putting the storm solidly into Category 5 status. The large eye of Ragasa is passing north of the large Philippine island of Luzon, though that region will be battered by significant winds over the coming day. This can be seen in the 10 min Himawari target imagery, which is following Ragasa as it progresses westward.

At this point Ragasa is projected to continue west-northwest and pass very close to Hong Kong. The past and projected track can be seen on the forecast graphic product from the Joint Typhoon Warning Center, issued at 0000 UTC on 22 September.

Additional information pertaining to Ragasa is available in this blog post.

View only this post Read Less

2.5-minute Target Sector JMA Himawari-9 Infrared images (above) showed Ragasa as it intensified from a Category 4 Typhoon at 0000 UTC on 21 September 2025 to a Category 5 (140-knot) Super Typhoon at 0600 UTC and then further to a 145-knot Super Typhoon by 1200 UTC (SATCON). There was a ~2 hour gap in Target Sector images, from 1100-1250 UTC; during that period, 10-minute Full Disk imagery was used to fill the gap.

The primary environmental factor that favored this intensification was low values of deep-layer wind shear (below) — in addition, Ragasa traversed a lobe of slightly warmer waters (Sea Surface Temperature | Ocean Heat Content) as it reached Category 5 intensity.

Ragasa was undergoing an eyewall replacement cycle (ERC) on 21 September, which was evident in the MIMIC-TC product (below) — the smaller-diameter inner eyewall was eventually replaced by a larger-diameter outer eyewall. However, the ERC did not adversely affect the intensity of the Super Typhoon during the course of the day.

3 snapshots of microwave imagery during the day (from DMSP/SSMIS and NOAA-21/ATMS) are shown below.

[the wind shear, sea surface temperature, ocean heat content and microwave products shown above were sourced from the CIMSS Tropical Cyclones site]

An RCM-3 Synthetic Aperture Radar (SAR) Wind Speed image (below) also highlighted a narrow “moat” of lower wind speed that was surrounding the inner eyewall at 2131 UTC (a “brightness temperature moat” feature was also seen in the 2152 UTC DMSP-17 SSMIS microwave image).

A sunrise-to-sunset animation of 2.5-minute Himawari-9 Visible images (below) revealed the presence of low-level mesovortices within the large eye. Super Typhoon Ragasa made its first landfall on the tiny island of Babuyan in the Luzon Strait after 0300 UTC on 22 September.

A Suomi-NPP VIIRS Day/Night Band image at 0511 UTC on 22 September — when Ragasa was still at Category 5 intensity (below) displayed the 40-mile diameter eye as its western edge was near Synoptic Station 981330 (Calayan Island).

The strong winds associated with Super Typhoon Ragasa caused high waves (above), which resulted in an upwelling of cooler sub-surface water in the northwest Philippine Sea — late in the day on 22 September (when Ragasa was located far to west, in the South China Sea), note the pocket of 27-28ºC Sea Surface Temperatures (yellow to light orange) along and north of the track of Ragasa at the point where it first reached Category 5 intensity from 0600-1200 UTC on 21 September (below). Sea Surface Temperatures over that area of upwelling were around 30ºC just prior to the passage of Ragasa.

As Ragasa was beginning to move west-northwestward away from northern Luzon on 22 September, a Significant Wave Height of 58.26 ft was sensed at 1352 UTC (below).

Additional information pertaining to Ragasa is available in this blog post.

View only this post Read Less

Transverse cirrus bands — narrow cirrus cloud filaments oriented perpendicular to the mean wind flow at the altitude of those cloud features — have long been recognized as indicators of potential aircraft turbulence. Such was the case on 20 September 2025, when a Mesoscale Convective System over Kansas/Oklahoma began to exhibit transverse banding along its northern to eastern periphery as it moved eastward toward the mid-Mississippi Valley (above). Several high-altitude pilot reports of light to moderate turbulence were seen in the area of transverse banding.

A stepped comparison of GOES-19 Infrared Window (10.3 µm), Upper-level Water Vapor (6.2 µm), Near-Infrared Cirrus (1.37 µm) and Red Visible (0.64 µm) images at 1301 UTC (below) showed that the transverse cirrus bands were best visualized using the Near-Infrared Cirrus and Water Vapor (and to a somewhat lesser extent, the Infrared) imagery — the presence low- to mid-level clouds tended to mask the appearance of some of the thin high-altitude cirrus bands.

Transverse cirrus bands are also occasionally observed near the axis of strong jet streaks and around the periphery of tropical cyclones.

View only this post Read Less