1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Infrared Window images (above) showed a large and persistent cluster of deep convection that remained southwest of Tropical Storm Bertha’s center during the nighttime hours leading up to sunrise on 23 July 2026.

Pulses of overshooting tops exhibited very cold infrared brightness temperatures of -90 C or lower (below).

1-minute GLM Flash Points (below) revealed prolific lightning activity associated with the large and persistent cluster of convection. The NHC Forecast Discussion at 0900 UTC mentioned that “there has been a persistent supercell thunderstorm with a mesocyclone moving westward through Bertha’s southwestern quadrant”.

Some of the GLM Flash Points exhibited an unusually long duration and large flash area (below). Over oceans, the average GLM flash duration is 0.345 sec, with an average flash area of 570 km² (reference).

While the official intensity of Bertha was 40 knots at that time, Ultra High Resolution ASCAT winds from Metop-B (below) showed 2 pockets of surface winds in excess of 50 knots (lighter shades of violet). These higher surface wind speeds may have been related to the aforementioned supercell thunderstorm with a mesocyclone.

A nighttime NOAA-20 VIIRS Day/Night Band image (below) displayed concentric mesospheric airglow waves (reference) that were propagating southward and westward from the large convective cluster. A few bright “lightning streak” signatures were apparent closer to the coast, which was where the core of the convective cluster was located. The Moon had already set over the western Gulf of Mexico prior to this time, so there was only atmospheric airglow to faintly illuminate any cloud features.

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1-minute Mesoscale Domain Sector GOES-19 Infrared Window images (above) showed Tropical Storm Bertha as it moved slowly northwestward then westward across the far northern Gulf of Mexico on 21 July 2026. Pulses of overshooting tops exhibited infrared brightness temperatures in the -75 to -80 C range (brighter white pixels). 1-minute GLM Flash Points displayed the lightning activity associated with deep convection near and south of the center of circulation.

1-minute GOES-19 Visible images (below) revealed that Bertha’s low-level circulation center (LLCC) remained partially to fully exposed during the day — since the tropical storm was moving through an environment characterized by high values of northeasterly deep-layer wind shear (1500 UTC | 2100 UTC), which acted to displace most of the deep convection south of the LLCC.

===== 22 July Update =====

1-minute GOES-19 Visible and Infrared Window images (above) showed that the fully-exposed eye of Tropical Storm Bertha moved inland across southeastern Louisiana after making landfall at 1900 UTC on 22 July. A small convective burst developed just south of the eye as Bertha moved inland. The highest wind gust associated with Bertha was 63 mph at METAR site KIKT.

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We are starting to see the onset of an active period of tropical development in the eastern Pacific basin. Over the weekend of 18-19 July 2026, two separate systems were experiencing different stages of their life: Elida was dying out near the west coast of Mexico while Fausto was starting to consolidate into a tropical storm. The following satellite loops from GOES-18 (GOES West) show these systems. The first is the Band 2 visible product. Elida is in the western center of the animation while Fausto is in the south central part of the loop.

Here’s the same loop as before, but from the Band 13 infrared perspective. Here, it is clear that Fausto represents deeper convection was the infrared imagery shows much colder cloud tops for that storm than it does for Elida.

Polar-orbiting satellites around this time provide some additional perspective on these storms. First, let’s look at some scatterometer data to evaluate near-surface winds. Here’s a view from OSCAT3 of Elida on Sunday the 19th. OSCAT tends to have more uncertainty in the wind vector retrievals than ASCAT does, but makes up for it with a wider swath and fewer gaps between swaths. (ASCAT was particularly unlucky with both storms on the 19th). Here we see clear evidence of a focused area of circulation with winds in the center maxing out at around 30-40 kts.

Going further south to Fausto at roughly the same time in the 19th, we see a circulation that is not quite as refined as Elida. Winds are slower and the center of circulation isn’t as circular.

Elida has propagated to the north, into the cooler waters of the midlatitude eastern Pacific. Between the 19th and the 20th, it lost its tropical storm status and is now officially post-tropical. However, Fausto is continuing to intensify and model tracks show that it may impact Hawaii in the coming days, so we’ll look at it a bit more. Here’s a frame from the CIMSS D-MINT product from 1930 UTC on the 19th, approximately the same time as the animated loops above). D-MINT uses microwave and infrared observations to assess the intensity of tropical cyclones. The left three panels show three different microwave channels, and forecasters can use these to more easily identify the center of circulation when the infrared or visible images are cluttered with high-level cirrus shields. Here we see the circulation is likely centered around the lower-left hand corner of the microwave images. The rightmost panel depicts the mean surface wind of the system as estimated by the D-MINT algorithm, and in this case it is around 30 kts.

We can use satellites to gauge how much Fausto improved from Sunday the 19th into Monday the 20th. We’ll start by looking at more recent scatterometer observations. In the ~25 hours between the OSCAT plot shown above and the more recent one below, Fausto’s circulation tightened up immensely and became much more circular.

We also see the intensification in D-MINT. This prodcut relies on available microwave satellite observations and not all satellites contain the same set of channels, hence the difference in the images shown here. Regardless, the algorithm now projects a mean surface wind of 44 kts by 1524 UTC, about 20 hours later than the image above.

NOAA’s National Hurricane Center projects that Fausto will become a hurricane on the 20th. Model forecasts, including the GFS and Google’s DeepMind show Fausto continuing to the east-northeast, weaking to a tropical storm just before it passes to the north of Hawaii. However, the long-term forecasts also show additional Pacific tropical systems developing south of Mexico and continuing to the east, so eyes will be on the Pacific for some time to come.

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Tropical Depression Two developed in the northeastern Gulf of Mexico at 1500 UTC on 19 July 2026 — and 1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible images (above) showed the slow trend of organization during the day (there was a 49-minute gap in image coverage as Mesoscale Sectors were rearranged). GLM Flash Points highlighted intermittent lightning activity associated with areas of deep convection. Tropical Depression Two was moving very slowly through an environment of relatively low wind shear, and was traversing warm water.

Metop ASCAT surface scatterometer winds at 1424 UTC (below) were generally at or below 25 kts — and wind gusts from nearby buoys and ships were also 25 kts or less in the animation shown above.

The corresponding 1-minute GOES-19 Infrared Window images (below) indicated that the coldest cloud-top infrared brightness temperatures of convection were generally in the -65 to -70 C range.

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