1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Visible images (above) and Infrared Window images (below) showed clusters of thunderstorms that produced hail as large as 2.50″ in diameter and wind gusts as high as 92 mph (SPC Storm Reports) across parts of South Dakota on 25 July 2026.

Pulses of overshooting tops exhibited infrared brightness temperatures as cold as -83 C (above) — which represented a significant overshoot of the Most Unstable (MU) air parcel’s Equilibrium Level (EL), according to a plot of rawinsonde data from Aberdeen, South Dakota (below).

1-minute GOES-19 Infrared Window images with plots of GLM Flash Points (below) displayed the abundant lightning activity associated with these severe thunderstorms.

View only this post Read Less

Earlier this week, we discussed the development of Fausto, a Pacific tropical system that formed south of Mexico. As expected, the storm has intensified to hurricane strength. Current projections (as of 1500 UTC, 5:00 AM HST) are for it to pass directly over the Hawaiian islands on Tuesday 28 July into Wednesday 29 July. Fortunately, the forecasts show the system weakening to a tropical storm before it reaches Hawaii, but the potential impacts for such a system are still quite significant given the potential for heavy rainfall. Here’s the most recent cone plot from the National Hurricane Center depicting Fausto’s expected track over the next five days.

The GOES-18 (GOES West) Band 13 infrared window imagery shows how Fausto has organized since the Blog last looked at it a few days ago. On Monday the 20th, it had a well-defined circulation but no eye was present in the infrared and even in the microwave it was somewhat challenging to identify exactly where the circulation was centered. Here on Friday 24 August, that’s no longer the case, as can be seen in the loop below.

If we take a close look at that loop, we seen that the eye is a little ragged and irregular. Compare this to when Bavi was at its greatest strength two weeks ago: its eye was almost perfectly symmetric. The strong correlation between hurricane form and its intensity is the heart of the Dvorak Technique for tropical cyclone intensity estimation. CIMSS has been a pioneer in developing automated methods of obtaining cyclone strength from satellites. The Advanced Dvorak Technique (ADT) assesses key parameters of the cyclone from infrared satellite imagery and thus can produce a continuous time series of cyclone intensity so long as there’s an accurate assessment of the position of the center of circulation. Here’s a time series of Fausto’s strength as calculated by ADT. Based on this, Fausto was a borderline Cat 2/Cat 3 event in during teh time shown in the above animation.

Since the development of ADT, CIMSS has continued to develop more advanced methods of retrieving tropical cyclone intensity from satellite observations. The D-MINT product is a deep learning algorithm that combines geostationary satellite data with microwave imagers and sounders from polar-orbiting satellites. Because it relies on the more temporally-infrequent microwave observations it doesn’t have the temporal continuity of ADT, but the enhanced inputs can contribute to a more accurate and reliable estimate, and each observation has an associated uncertainty with it. Here’s the D-MINT time series for Fausto.

With many different automated methods for cyclone strength estimation, it is convenient to see these methods together. The CIMSS SATCON product takes estimates from several different sources and produces a weighted average consensus value. Here, we see a consensus of around 95 knots as of the most recent estimates.

Scatterometry and synthetic aperture radars also provide compelling views of the structure of tropical cyclones. The wide spacing of the scatterometer swaths in the tropics can sometimes prove frustrating as the center of a cyclone can frequently be in the gaps. However, the most recent MetOp-C ASCAT scatterometer overpass was dead on and captured the wind structure perfectly. Note that the observed wind speed tops out at 50 kts, much lower than the automated wind speed estimates described above. This is a limit of the instrument itself and thus we cannot rely on it for exact measurements of wind speed within the core of a tropical storm. However, it is still quite valuable to see the overall distribution of winds and the general flow patterns around the center of circulation.

Synthetic aperture radar (SAR) winds can provide much more detail on the wind speed of a tropical system, with higher maximum values and much higher spatial resolution than the ASCAT method seen above. Below is a plot we see courtesy of NOAA STAR. Here we see winds approaching 100 kts on the north side of the eye. This provides an excellent depiction of somethingwe expect: in the northern Hemisphere, winds on the right side of the eye relative to the direction of motion are faster than those on the left side. This is because the winds on the right side are abetted by the motion of the storm itself while those on the south side are counteracted by storm motion. Note that the SAR product doesn’t directly show wind direction; the SAR technique can only be used for the magnitude of the wind, not its direction. The STAR plot embeds modeled wind vectors to bring context about wind direction to the plot.

Current forecasts show that Fausto is near its peak intensity and weakening is expected over the next few days. Some additional notes from the National Hurricane Center said in its 5:00 AM HST (1500 UTC) discussion:

However, it is worth noting that the guidance has 
struggled to capture the trends in Fausto's intensity over the past 
few days.  Nonetheless, decreasing water temperatures and drier air 
should cause the cyclone to gradually lose strength, and an increase 
in westerly vertical wind shear early next week will likely aid in 
that weakening trend.  The NHC intensity forecast lies near the 
middle of the guidance envelope, and shows steady weakening through 
the period.  There is relatively high confidence that Fausto will be 
a tropical storm when it is in the vicinity of the Hawaiian Islands.

View only this post Read Less

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.

View only this post Read Less

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.

View only this post Read Less