Night Microphysics RGB imagery from the CSPP Geosphere site (link) show the blossoming of high clouds (deep red in the RGB) north of the Samoan Islands, clouds that subsequently sag southward. Careful inspection of the animation also shows clouds that are more pink than deep red; these are likely mid-level clouds that might be developing in the vertical. Water vapor imagery (below, from this site) also show the development of cold cloud tops north of the Samoan Islands, part of a region of colder cloud tops that extends to the east of American Samoa (circled in this annotated water vapor image from 1320 UTC).

As you’re pondering the satellite imagery, perhaps you recall the numerical models from the previous days. The animation below (taken from the tropicaltidbits website) shows precipitation moving towards the Samoan Islands (in the upper right quadrant of the domain) from the east and northeast. This animation shows a nine sequential forecasts all valid at 0600 UTC on 28 January 2025. The forecasts were consistent in bringing rain towards the Samoan Islands (near 12^oS, 170^oW). And the satellite imagery above shows convection dropping southward.

A timely Metop-C overpass provided ASCAT sea-surface winds at 0930 UTC over the Samoan Islands. Strong winds to the north of Samoa, and lighter winds near Samoa, suggest surface convergence that might be helping to force the convection. (Image from this website).

LightningCast Probabilities (available here) show the likelihood of a GLM observations within the next 60 minutes. The animation below shows LightningCast increasing to the north of the Samoan Islands overnight on early 28 January; those probabilities move southward as convection continues, and eventually lightning (in the form of GLM Observations) occurs over Independent and American Samoa. The lightning is north of American Samoa at 1040 UTC, and overspreads the islands from 1140-1410 UTC, when the animation stops. (Click here for an animation with a faster timestep). The increasing LightningCast probabilities suggest strong convection .

Pago Pago, American Samoa reported light rain at 1600 UTC on 28 January. When you try to determine if rain is imminent, use as many satellite products as you can!

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