Heavy rains developed overnight over American Samoa, as depicted by the animation above from the CSPP Geosphere site. Low clouds — white/cyan in the RGB — start to show vertical development (that is, they get more and more red) shortly after 1000 UTC with more vigorous vertical growth apparent after 1100 UTC. Pago Pago on the island of Tutuila has had a particularly wet month: 25″ of rainfall through 27 May, which is the second wettest May on record there (data from here). What clues were present to help anticipate this convective development? The animation below shows GOES-18 Clean Window infrared (Band 13, 10.3) imagery from 1000-1400 UTC, and it is overlain by GOES-18 estimates of Lifted Index (scaled from -5 to 4). American Samoa is at the northern edge of a pool or greater instability that is available given a suitable trigger.

Sometimes, LightningCast probability fields (available here) can give a suitable warning of convective development (and, subsequently, lightning) as discussed in this blog post (and elsewhere): that is, contours start to appear with convective initiation. Convective development on 28 May was quite rapid. Lightning occurred within about 20 minutes of the first contour appearing just south of Tutuila in the animation below. In other words, LightningCast in this case was helpful in alerting a forecaster that convection was developing — but that signal was also apparent in single-banded imagery!

At 1330 UTC (the middle of the night in American Samoa), a Flash Flood Warning was issued for American Samoa.

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Interleaved 1-minute Mesoscale Domain Sector and 5-minute CONUS Sector GOES-19 (GOES-East) Upper-level Water Vapor images (above) displayed the SpaceX Starship 9 rocket exhaust plume thermal signature after it was launched from the Starbase facility at Boca Chica Beach, Texas at 2336 UTC on 27 May 2025. Note the change in exhaust plume shape with time and atmospheric layer: at early altitudes of 20-50 km (where atmospheric gases within the Stratosphere had more density, and therefore higher ambient pressure), the Stage 1 Super Heavy booster plume was more linear — but after the 2339 UTC “hot stage separation” as the Stage 2 rocket reached higher altitudes of 70-100 km (where atmospheric gases within the Mesosphere and Thermosphere were much less dense, with lower ambient pressure) the plume was able to expand outward into more of a curved “boomerang” shape beginning at 2341 UTC.

The changing shape of the exhaust plume with time (and altitude) was also apparent in 1-minute GOES-19 Plume RGB images created using Geo2Grid (below).

A display of all 16 ABI spectral bands from GOES-19 (below) showed that a hot thermal signature of the Starship booster was apparent in Near-Infrared & Infrared bands 04-16 — especially 1 minute after launch (at 2337 UTC) near the coast. In addition, the rocket booster exhaust condensation cloud was seen in all 16 spectral bands, as it began to drift eastward away from the Starbase launch site.

A toggle between zoomed-in 16-panel GOES-19 images at 2336 and 2337 UTC (below) made it easier to see the distinct Super Heavy booster thermal signature in spectral bands 04-16 at 2337 UTC.

1-minute GOES-19 True Color RGB images from the CSPP GeoSphere site (below) displayed the rocket booster condensation cloud as it drifted eastward away from the Texas coast.

10-minute Full Disk scan GOES-18 (GOES-West) True Color RGB images (below) also provided a brief glimpse of the rocket condensation cloud as it cast long shadows onto to offshore waters.

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Imagery from the CSPP Geosphere site (link), above, shows an area of disturbed tropical weather to the south of Mexico in the eastern Pacific Ocean. The National Hurricane Center (link, and below) notes a lack of organization with slow development forecast over the next few days. (Note that GOES-West Mesoscale Sector #2 is monitoring this region. Here’s a 1-hour animation.)

Metop-B overflew the system at 0400 UTC on 27 May, as shown below (source). A possible circulation center — or perhaps better stated as a center of cyclonic vorticity — is apparent at the southwestern edge of the domain near 11^oN, 100^oW.

In what kind of environment does this disturbed weather find itself? Imagery from the SSEC/CIMSS Tropical Weather site, below, shows relatively low values of wind shear, and very warm Sea-Surface Temperatures. In addition, low-level convergence and upper-level divergence are very close to the vorticity maximum at 850mb. A second set of scatterometery, from HY-2C (also available at this KNMI website), shows the broad center of circulation.

A 24-hour animation of MIMIC Total Precipitable Water, below, shows that this system is embedded within the abundant moisture of the Intertropical Convergence Zone.

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This invest is in a moisture-rich environment, with warm sea-surface temperatures and fairly low shear. Slow development is forecast. For more information on this system, refer to the SSEC Tropical Website, or the website of the National Hurricane Center.

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Clear skies over the Gulf of Maine close to midnight early on 27 Man 2025 allowed for the VIIRS instrument on NOAA-20 to capture a crisp view of the sea surface temperatures over that body of water. Temperatures are cooler than 50^oF over the entire Gulf of Maine, with low 40s (magenta in the color table used) hugging the coast of eastern Maine and Atlantic Canada. The coldest temperatures — in the 30s, still! — are over Lake Ontario. At the very southern edge of the scene, the warm waters of the Gulf Stream (just a bit warmer than 80^oF) are apparent.

JPSS data used in this blog post downloaded at the SSEC/CIMSS Direct Broadcast antenna and processed into AWIPS-ready tiles by CSPP software.

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