Clean-window infrared imagery centered on the Samoan Islands on 9 March 2025, above, show convective development north of Upolu that subsequently shows a cyclonic circulation. This system was accompanied by Flood Warnings, Heavy Rain Warnings and Marine Warnings and Wind Advisories over all of Samoa (Facebook link). Gusts exceeding 70 km/hr were reported. A very timely MetopC overpass, below (courtesy Joe LaPlante from the NWS in Pago Pago), shows the low-level circulation that developed. It does not appear to have cut off into a closed circulation at that time.

How well can a strong spin-up like this be anticipated? A deterministic ECMWF forecast initialized on 0000 UTC on 8 March, below, showed a region of active weather moving southward through the Samoan Island chain after 1800 UTC on 8 March. Note the small box drawn around the Samoan Islands. (Here is the 1200UTC/8 March ECMWF run that shows a similar evolution). Imagery is taken from the excellent TropicalTidbits website.

Deterministic models from the GFS (imagery also from the Tropical Tidbits site), below, show a similar scenario, both from the model initialized at 0000 UTC/8 March below, and the one starting at 1200 UTC/8 March at this link. All of the forecasts show a system sagging towards the south across Samoa.

MIMIC Total Precipitable Water (TPW) fields from 0000 UTC 8 March through 1200 UTC 9 March 2025, below (from this site), suggest a local maximum in moisture over the islands, and the fields also show the southward motion.

Visible imagery (from the CSPP Geosphere website) below shows active weather north of Samoa. It moves south throughout the animation.

Now consider the Metop-B ASCAT winds below, from ca. 2100 UTC on 8 March 2025. A local maximum in wind (in red) is north of Savai’i, and the leading edge of a region of stronger winds. Is this single observational plot sufficient for a forecaster to prepare the weather that was observed?

The GOES-18 imagery at that time (pulled from the visible animation above) shows strong convection (circled in black) near that region of stronger winds. If you trace that convective region southward to Upolu and Savai’i, does it overspread the region that saw damage (downed trees, taken from here, for example) and heavy rain?

Clean window infrared imagery, below (the end of the animation below overlaps with the start of the infrared animation shown above), suggests that perhaps that region of strong winds in the ASCAT fields, if associated with strong convection can be tracked to the south.

Once the cyclonic circulation is apparent, would you expect it to persist in the environment? That is — are we seeing the development of a tropical cyclone? Shear values (from the CIMSS Tropical Weather Website), show a narrow region of favorable shear where the spin-up occurred. Like the forecasts and other fields, the favorable shear region is shifting south with time.

Upper-level divergence is similarly shifting southward, with strong values where the convection and spin-up occurred.

Low level convergence fields also show a southward progression, but are not as organized as upper levels. Maybe that’s why this cyclone did not persist with time.

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Thanks to the Forecast Office in Pago Pago for alerting me to this interesting event.

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Early this morning at around 3:15 AM local time, an EF-0 tornado touched down in Pico Rivera, a community in Los Angeles County, California. It damaged several homes and knocked down numerous trees over the course of its mile-long path. Numerous instances of damaging winds were also reported, as seen on the NOAA SPC Storm Reports page. Fortunately, there were no reports of injuries.

Tornadoes in Los Angeles County are comparatively rare, but not unheard of. This is the 50^th recorded tornado in the county since 1950, and every month of the year has had at least one tornado report. The peak season for LA County tornadoes is winter and spring with more tornadoes recorded in January than any other month; with today’s event, March is now tied for second on that list. The NOAA NCEI Storm Events Database is an invaluable tool for analyses like these.

This particular storm event was driven by an advancing cold front linked to a low pressure system offshore. A steady stream of moist air from the Pacific ensured sufficient moisture to support convection. That is evident in the GOES-18 Band 8 upper level water vapor imagery, which shows a plume of moisture pointed directly at the greater Los Angeles area.

A polar-orbiting overpass at 0930 UTC (2:30 AM local time, approximately 45 minutes before tornadogenesis) provided Gridded NUCAPS observations. The 700-500 mb lapse rate product from Gridded NUCAPS shows lapse rates over LA County to be close to the critical conditionally unstable value of 6.0 C/km, with more unstable air aloft coming onshore from the south. The elevated lifting from the advancing front coupled with the elevated instability was enough to support deep convection.

Forecasters anticipated the potential weather overnight and the GOES-18 mesoscale sector was active for this event, providing images every minute. Since it was nighttime, none of the products that depend on shortwave channels were available, but many interesting things can be discerned from the longwave imagery. The Channel 13 IR window view shows the cold cloud top temperatures associated with the deep, moist convection, while the speckled orange portions of the Night Microphysics RGB help to confirm that the clouds over LA are deep, thick, and moisture-laden. Mesoscale sectors are available in AWIPS, or are freely available to everyone at SSEC RealEarth.

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W-NW winds gusting in excess of 50 mph in the wake of a cold front lofted areas of blowing dust across parts of Texas on 12 March 2025, as seen in GOES-16 (GOES-East) Visible images (above). Blowing dust reduced the visibility to 1-1/2 miles at times along the Interstate 20 corridor in the vicinity of Midland.

Daytime True Color RGB images created using Geo2Grid (below) provided a more distinct view of the blowing dust — and after sunset, Dust RGB images highlighted the airborne dust as shades of magenta.

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A sequence of Suomi-NPP VIIRS Visible images (above) showed the formation of large ice leads in the eastern Beaufort Sea — as well as the growth of a polynya adjacent to the coast near the Alaska/Yukon border — during the 5-day period from 07-11 March 2025.

Suomi-NPP VIIRS Shortwave Infrared images (below) provided a view of the ice leads and polynya during both the nighttime and daytime hours during the 07-11 March period.

Daily composites of Suomi-NPP VIIRS Sea Ice Temperature/Thickness/Age products (source) indicated that the larger ice leads were developing near the gradient of temperature and thickness of old ice in the eastern Beaufort Sea (below).

In spite of lower spatial resolution and a large satellite viewing angle, the more prominent ice leads (as well as the polynya adjacent to the Alaska/Yukon coast) were also apparent in GOES-18 (GOES-West) Visible images from the CSPP GeoSphere site (below).

Comparisons of Ice Stage and Ice Analysis (source) shown below indicated that the 2 largest ice leads and the polynya formed during the 7-day period between 03 March and 10 March.

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