Deep Convection and Strong Lightning Near American Samoa
The early morning hours of 21 February 2026 brought some intense tropical convection to the vicinity of the Samoan Islands. Radar coverage is lacking in this part of the world so satellites remain the best way to monitor storms in this region for potential safety hazards. A good first stop is checking the NUCAPS vertical profiles for a location to gauge the potential for convective instability. Since this post was written a few days after the event in question, our standard sources for NUCAPS profiles no longer have the relevant data, but the NOAA OSPO HEAP site allows us to go back 20 days to review the satellite-observed skew-T profiles. American Samoa is in the UTC –11 time zone (almost as far away from UTC as one can get) so this profile is around 1:20 AM local time. NUCAPS profile retrievals are applied to collocated infrared and microwave sounder observations. The microwave (MW) observations are able to see through the clouds but lack the vertical resolution of the infrared (IR) observations. The highest-quality profiles include both the MW and IR, but if the clouds are too thick, the retrieval algorithm will default to the MW only. The following plot shows both the MW-only (blue) and the MW+IR (maroon) profiles.
It’s interesting to see how the two different methodologies result in two very different levels of instability. The MW only retrieval has a CAPE of 3643 J/kg while the MW+IR retrieval brings it down all the way to 0. The biggest difference between the two appears to be differences in near-surface temperatures and the presence of a mid-level inversion between 600 and 800 hPa. However, those low-level temperatures appear to be an underestimate, especially for the MW+IR retrieval. At 1200 UTC, the surface temperature and dew point at the Pago Pago, AS, airport were 30/25 C respectively. That’s much warmer than NUCAPS estimated. If you append those values to the bottom of the sounding (the mean surface level pressure was 1005 hPa, and since the elevation of the airport in Pago Pago is just a few meters above sea level, the station pressure is basically the same as MSLP) you’ll see that the profile becomes much more positively buoyant. Here’s a hand-drawn illustration of that, with the new temperature and dew point added in red and the corresponding area of positive buoyancy shaded in orange. At the very least, it is likely that the CAPE value measured by the microwave-only retrieval is closer to the truth than the 0 value returned by the MW+IR retrieval.
LightningCast captured the potential for significant lightning from this storm. The following animation shows the LightningCast contours overlaid on top of the Band 13 infrared imagery from GOES-18. The occasional blue patches represent the GLM-observed flash density, helping to verify LightningCast’s predictions.
The deep reds of the Night Microphysics RGB also help indicate the presence of deep, thick convective clouds.
Together, the thermodynamic observations from the polar-orbiting satellite and the continuous, time resolved imagery from the geostationary perspective help offer a comprehensive portrait of the intensity of this event.