1-minute Mesoscale Domain Sector GOES-19 (GOES-East) Infrared Window images (above) included Flash Flood Warning polygons and 1-hour precipitation accumulations during a period when thunderstorms produced heavy rainfall and flash flooding across parts of the Northeast US on 20 August 2026. Notable rainfall occurred in the New York City area, with over 5 inches recorded in Suffolk County on Long Island; the highest 1-hour precipitation accumulation at nearby La Guardia International Airport was 1.82 inches.

Some of these thunderstorms also produced tornadoes and damaging winds — 1-minute GOES-19 Visible images (above) and Infrared Window images (below) included time-matched plots of SPC Storm Reports.

The thunderstorm that produced a tornado in Dover, Delaware exhibited a well-defined Enhanced-V storm top signature (below).

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Earlier this week we introduced you to Lala, a Pacific tropical cyclone. In our first post, Lala was a tropical storm that was setting its sights on Hawaii. Some interesting things have happened since then. First, Lala strengthened to hurricane intensity as it approached the big island of Hawaii. Here’s an animation of the true color view from GOES-18 (GOES West) as the eye passed just to the south of the Big Island. Note that this storm has the visual hallmarks of a weaker tropical cyclone, including an obscured eye.

Of course, just because it’s a weaker storm doesn’t mean it’s not a dangerous storm. Given the westerly trajectory of Lala, the strongest winds are going to be be on the north side of the system where the cyclonic flow is pushing with the storm’s motion instead of on the south side where the flow is acting opposite to the storm’s motion. The impact of this flow was notable, and the NCEP storm summary is astonishing: 140 mph wind gusts at Mauna Kea, hurricane-force winds throughout Hawaii, over a dozen stations with more than two feet of rain. Hundreds of thousands of Hawaiians were without power, and flash floods tore through the islands’ rugged terrain. But perhaps no impact captured the imagination of mainlanders quite like the the snowfall experienced on Hawaii’s highest peaks. Hawaiian snow isn’t altogether rare, as we discussed in this post back in February. August is a little different, however, and this was extremely atypical behavior. However, for most deep storms including hurricanes, the clouds are so deep that precipitation starts out as snow before melting into rain as it falls. With tropical cyclones, most of the time there isn’t a 13,800 foot tall mountain in the way to be hit by one of the rain bands and so we never see this snow before it has the chance to melt.

Consider this sounding from Hilo on the Big Island at 0600 UTC on the 16th (8:00 pm local time on the 15th), taken as the hurricane was passing by to the southwest and archived by the invaluable University of Wyoming Atmospheric Science Radiosonde Archive. This is a typical tropical cyclone profile, with saturated air all the way through the troposphere and strong winds all the way to the surface, and wind that shifts from blowing toward the low at the ground (convergence) to blowing away from it aloft (divergence). But look at that freezing level: it’s around 550 mb or 5140 m. While that’s still almost 1 kilometer above the height of Mauna Kea, the slow lapse rate in this saturated and well-mixed environment means that the temperature at the mountain’s peak is only a couple of degrees warmer than freezing. Snowflakes could easily have formed at the higher levels and not completely melted before reaching the surface at this significant altitude.

While Lala dished out a blow to the people of Hawaii, it didn’t emerge unscathed. The interactions with the terrain scoured the storm of some of its momentum, and it dropped back down to tropical storm status. It’s mid-August, however, and so the waters to the southwest of Hawaii are typically warm. This year, those waters are also 0.5 to 1.0 degrees C above normal thanks to being on the outermost periphery of El Niño as can be seen on the below map. This puts the sea surface temperatures in the area around 80-82 F, which is plenty warm for tropical development.

Maneuvering into a warm sea and low-shear environment was beneficial for Lala’s development, and it rapidly intensified. From 0000 UTC on the 18th to 24 hours later, it strengthened from a strong tropical storm all the way to a weak Category 4 hurricane. The time series of automated intensity estimates from the CIMSS D-MINT product tells the story well.

As of 1400 UTC on the 19th, Lala is straddling the line between Category 3 and Category 4. One of the mesoscale sector scans from GOES-18 has been trained on it, so it’s possible to see it evolve on a minute-by-minute scale. Here is an animation from around 1430 UTC of the Band 13 infrared window channel. It’s night at this time, so no shortwave products are available. Still, this is an excellent way to assess just how intense this storm is. There’s a clear, well-defined eye that even has a hint of some mesovortices in the inside. The cold thick clouds have the classic cyclonic rotation to them while the outer cirrus bands are exhibiting the anticyclonic spin of the divergent flow aloft.

Lala’s westward progression is projected to end as it’s forecasted to make a northward turn. Fortunately, while it is still a major hurricane its current path is taking it over the open ocean and its impact on lives and property is expected to be minimal.

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10-minute Full Disk scan GOES-18 (GOES-West) GeoColor RGB images with an overlay of Next Generation Fire System (NGFS) Fire Detection polygons (above) showed the thermal signature associated with the Mukluk Fire near Tok, Alaska — which began around 1940 UTC on 17 August 2026. With winds at Tok gusting to 20-30 mph, the fire spread quickly and forced some evacuations in the Tok area (18 August update).

10-minute GOES-18 Visible images with an overlay of the Fire Mask derived product (below) provided another view of the fire’s thermal signature.

The areal coverage of NGFS Fire Detection polygons was somewhat distorted in GOES-18 imagery, due to the large effective pixel size of the spectral bands used to create the NGFS product (as shown in a plot of pixel size vs. satellite viewing angle; the GOES-18 viewing angle or zenith angle for Tok is around 72 degrees). Polar-orbiting satellites such as NOAA-20 and NOAA-21 flew directly over Alaska as the Mukluk Fire was burning, and offered a more accurate mapping of the fire’s thermal signature (below).

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The first half of August 2026 has brought repeated heavy rainfall to the state of Indiana, with the area in and around the capital city of Indianapolis experiencing particularly strong flooding. Numerous roads are closed, and a bridge in Carmel, IN, just north of Indianapolis, has been washed out. Multiple fatalities have already been reported, and continued storms on Sunday 16 August are exacerbating an already challenging situation.

A sustained river flooding event builds over an extended period of time, and this event is no exception. We’ll start our analysis by looking at the cumulative rainfall graph for Indianapolis dating back to 31 July 2026 as recorded by the invaluable xmACIS2 site. So far in August 2026, Indianapolis has seen three separate days with at least one inch of rainfall, including a whopping 2.09 inches on the 1st of the month. As a result, Indianapolis has experienced more than twice the normal amount of rainfall up to this point in August.

All of that water has to go somewhere, and so it rushes into the streams and rivers of Central Indiana. This plot shows the time series of water flow in the White River just north of Indianapolis dating back to August 1, roughly contemporaneous with the precipitation graph above. Note the logarithmic scale. It’s easy to see how the initial heavy rainfall on the 1st caused the water levels to rise and the flow rates to increase over the next few days, but an extended period of over a week without rain caused a gradual slowdown in the water flow. However, once the rain returned it came back in a big way and the water levels quickly exceeded the system’s capacity to absorb them. Between the 11th and the 15th flow rates increased by a factor of 70.

Perhaps the most important question is: what’s been causing all this rain? Here’s where our satellite tools can provide valuable insight. The CIMSS MIMIC-TPW2 product helps identify areas of elevated moisture by compositing microwave observations of total precipitable water (TPW) with gridded wind data to depict how the moisture evolves over time. Recall that TPW is the measure of how much precipitation in a column of air could be produced if all of the water vapor in that column condensed into liquid and fell to the ground.

Here’s the TPW plot for the contiguous United States on 1 August at 0000 UTC (31 July at 8:00 PM EDT) showing the state of the atmosphere just ahead of that 2 inch rainfall day. Note the strong moist plume that runs up the lower Mississippi valley and into Illinois and Indiana. These TPW values are nearly tropical in magnitude. (That’s no exaggeration: compare the values of the TPW in the Midwest to the bullseye of Tropical Storm Genevieve around 20 N 130 W).

Similarly high levels of TPW have been present over the past several days. Here’s an animation of the CIMSS MIMIC-TPW2 product for Sunday 16 August, covering the most recent round of storms over Indiana. Again, these storms have quite high TPW values, which are made possible by warm August air with a high capacity for elevated moisture levels, significant moisture advection from the Gulf, and high transpiration from the Midwest’s corn fields.

Let’s take a closer look at the most recent round of storms to hit central Indiana. The GOES-19 (GOES East) true color view shows a band of deep moist convection heading east-southeast from Illinois into most of central Indiana. Numerous overshooting tops are visible which become easier to see as the loop goes on; this is more likely due to the setting sun casting longer shadows than it is any trait of the clouds themselves.

The IR sandwich product can be a quite useful tool for assessing the strength of daytime convection. In the IR sandwich, colors representing the infrared window brightness temperatures are overlaid on top of the high resolution visible channel. Lower (warmer) clouds remain unshaded, but deeper (colder) clouds have colors associated with them. Since the overshooting cloud tops are going to be the coldest parts of the cloud, they’re going to appear as a different color. This makes the clouds appear to have more texture than the true color product shows, making it easier for forecasters to identify where the most vigorous convection is. In essence, this unites some of the best aspects of the visible band (high spatial resolution) with the infrared (quantitative information about cloud temperatures).

Satellites can also help identify where the flooding is taking place. Back in July, the CIMSS Satellite Blog discussed the ABI Flood Mapping package deployed by the CSPP Geo group. In short, by comparing geostationary observations of surface water and comparing those to a baseline level of known bodies of water, it’s possible to determine the extent of surface flooding. By applying this technique to the geostationary ABI instrument, forecasters and hydrologists can track flooding on fine timescales and, perhaps more importantly, be more likely to dodge the clouds that would otherwise inhibit the observations. Here’s an animation that shows how that works in practice. This animation stretches from 1500 to 2000 UTC on 16 August 2026 (11:00 AM to 4:00 PM EDT). Tan represents dry land, gray depicts missing data due to clouds, and blue shows where surface water is expected. The other colors represent various degrees of flooding. As the clouds clear we see flooded areas emerge in central Indiana, especially around the White River which cuts northeast to southwest across Indianapolis and central Indiana.

Both the IR sandwich and the ABI Flood Mapping products are available from SSEC’s RealEarth data viewer.

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