Overlapping 1-minute Mesoscale Domain Sectors provided GOES-19 (GOES-East) images at 30-second intervals — Infrared Window imagery (above) showed Hurricane Isaias moving toward the US Gulf Coast on 09 October 2026. Isaias reached Category 3 intensity at 1220 UTC (Infrared image | NHC advisory). The coldest cloud-top infrared brightness temperatures were in the -85 to -88 C range (darker shades of purple). GLM Flash Points displayed occasional lightning activity within the core of Isaias.

Although Isaias was moving through an environment of rather high southwesterly vertical wind shear (below), the shear direction generally aligning with the storm motion likely helped to mitigate unfavorable shear effects.

Isaias passed over a patch of fairly high Ocean Heat Content (below), which may have played a role in its intensification to Category 3.

While Isaias was still a Category 2 storm, a well-defined eye was depicted in microwave imagery from ATMS and DMSP-18 (below).

Wind shear, ocean heat content and microwave imagery was sourced from the CIMSS Tropical Cyclones site.

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A closer view of 30-second GOES-19 Infrared Window images (below) showed Category 3 Hurricane Isaias as it approached the Gulf Coast and eventually made landfall near Destin, Florida (METAR identifier KDTS) at 0130 UTC on 10 October (weakening to a high-end Category 2 storm just prior to landfall). After landfall, GOES-19 cloud-top infrared brightness temperatures warmed and GLM-based lightning activity decreased.

Shortly after the time of landfall, Isaias produced a wind gust of 99 knots (114 mph) at Whiting Field Naval Air Station KNDZ (below). A list of wind gusts included 117 mph at Oriole Beach.

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Tropical Storm Isaias reached hurricane intensity at 0330 UTC on 08 October 2026 — becoming the first Atlantic Basin (which includes the Gulf of Mexico) hurricane of the 2026 season. 1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Infrared Window images (above) showed the deep convection in the vicinity of the surface storm center of Hurricane Isaias — with GLM Flash Points displaying lightning activity with many areas of deep convection. The coldest cloud-top infrared brightness temperatures associated with convective bursts near the storm center were in the -85 to -90 C range (darker shades of purple).

In an animation of 1-minute GOES-19 Visible images (below), a gradual thinning of high clouds over the storm center eventually revealed an eye for a few hours later in the day.

Isaias continued to intensify to a Category 2 storm by 1800 UTC, in spite of moving through an environment of moderate southwesterly vertical wind shear (below).

A DMSP-18 SSMIS Microwave image (below) depicted a large (albiet somewhat ragged) eye.

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1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Infrared Window images (above) showed Tropical Depression Nine on 06 October 2026 as it eventually developed into Tropical Storm Isaias in the southern Gulf by 0900 UTC on 07 October. Plots of GLM Flash Points depicted the lightning activity within the slowly-organizing tropical storm. The coldest cloud-top infrared brightness temperatures associated with convective bursts were around -90C.

Tropical Depression Nine was embedded within an environment of modest vertical wind shear, as seen in Visible images (above) and Infrared Window images (below).

===== 07 October Update =====

After Isaias reached Tropical Storm intensity at 0900 UTC on 07 October, 1-minute GOES-19 Infrared Window images (above) showed that most of the deep convection generally remained north/northeast/east of the storm center — although there were periodic convective bursts closer to the center of circulation (especially after about 2000 UTC). Lightning activity was associated with many areas of deep convection.

An ATMS microwave image at 1931 UTC (above) depicted an arc of convection that was wrapping around the northern, western and southern edges of the center of Isaias — while a DMSP-18 SSMIS image at 2225 UTC (below) suggested that an eye might be developing (and the 0300 UTC NHC discussion mentioned that hurricane hunter aircraft found a circular eyewall, partially open to the SW).

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Once again, we see that 2026 continues to bring a large number of tropical systems in the Pacific. This time, we turn our eyes to the western part of our planet’s largest ocean to see a trio of tropical cylones in action. On the morning of 6 October 2026, three separate tropical systems were actively churning in the western Pacific Ocean. These systems included Typhoon Choi-Wan, the continuing Typhoon (former Hurricane) Nolo, and Tropical Storm Koguma. Here’s a large-scale true color view from Himawari-9 showing all three systems. Choi-Wan is the large storm near Japan in the northwest of the animation, Nolo is the more compact system in the east-central part of the animation, and Koguma is the small and not-yet-organized storm in the south central portion of the loop.

While there is a convective mass in the southwest part of the loop that is, in fact, larger than Koguma, the animation shows strong vertical shear with lower level and upper level windows in basically opposite directions. It also doesn’t appear to have any circulation characteristics, so in the end it doesn’t appear to be a typhoon-in-waiting.

A look at the contemporaneous Band 13 infrared animation helps bring a little more definition to these storms. It’s easier to see the circulation around Koguma, for example, and the lack of circulation associated with the convective system in the southwest.

Choi-Wan actually peaked at Category 5 status, joining the notorious list of 20206 Category 5 super typhoons that included Sinlaku, Bavi, and Dolphin. The synthetic aperture radar (SAR) winds from the 4th show an almost perfectly symmetrical wind field with magnitudes well over 100 knots.

The D-MINT time series of Choi-Wan shows a pretty steady intensification rate, peaking at Category 5, and then a consistent weakening after that. There was no obvious eyewall replacement in this storm like we’ve seen with some of the other strong typhoons this year.

By comparison, the D-MINT time series of estimated cyclone strengths for Nolo has been quite fascinating. As reported on the blog, Nolo started out as an eastern Pacific hurricane but crossed the 180 degree longitude line to officially be classified as a typhoon. While it was still in the east, Nolo got very close to Category 5 status, but its northerly trajectory at that time took it into a relatively cooler region of water and so it weakened into a tropical storm. However, it took a westward turn and into fresher waters which reinvigorated it, and it strengthened back to a Category 3.

As far as the weakest of the three systems, Tropical Storm Koguma, while it is over warm water, it’s also experiencing dry air entrainment and is somewhat vertically tilted. Therefore, the Joint Typhoon Warning Center is predicting a marginally favorable environment for continued development.

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