1-minute Mesoscale Domain Sector GOES-18 (GOES-West) “Clean” Infrared Window (10.3 µm) images (above) displayed a period of convective bursts near and over the American Samoa island of Tutuila on 04 February 2024 — which produced heavy rainfall (leading to flash flooding and landslides; during the 6-hour period ending at 1200 UTC, Pago Pago recorded 3.92 inches of rain), strong winds (gusting to 38 kts or 44 mph at Pago Pago, with wind gusts elsewhere estimated to 50 mph) and power outages across parts of the island (Local Storm Reports). The coldest cloud-top infrared brightness temperatures were in the -90 to -93ºC range (shades of purple embedded within brighter white regions) — which indicated that the stronger overshooting tops were ascending past the local tropopause, according to Pago Pago rawinsonde data.

These convective bursts developed as Tropical Disturbance TD06F was slowly approaching American Samoa (Fiji Meteorological Service surface analyses: 0300 UTC | 0600 UTC | 1200 UTC); TD06F continued to organize and intensify, eventually becoming Tropical Storm Nat at 1200 UTC on the following day (see this blog post for more information).

A GOES-18 Infrared image at 0710 UTC (below) included cursor sampling of the associated Level 2 derived product Rain Rate, Cloud Top Phase and Cloud Top Height — the derived Rain Rate at that cold (-92ºC) overshooting top was 3.94 inches per hour.

A larger-scale view during the 3-day period from 02-04 February is shown below. Clusters of deep convection first affected the islands of Western Samoa, before later forming over American Samoa. The South Pacific Convergence Zone (SPCZ) remained in the vicinity of the Samoan island chain during that time (1200 UTC surface analyses: 02 Feb | 03 Feb | 04 Feb), helping to focus convective development..

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All 4 components of the GOES-16 (GOES-East) Fire Detection and Characterization Algorithm (FDCA) (above) showed the diurnal variability of thermal signatures associated with a large and deadly wildfire complex near Viña del Mar and Quilpué in the Valparaíso District — located along the central coast of Chile — from 02-04 February 2024 (maximum Fire Power values occasionally reached 2200-2300 MW). After the wildfires began around 1510 UTC on 02 February, they spread northward rather quickly (due to strong southerly winds) — until an influx of cooler and more moist Pacific air early on 04 February helped to suppress the fire behavior. The METAR site plotted in the imagery is Santiago International Airport (where daytime air temperatures rose into the 90s F on 02/03 February).

A larger-scale animation of the FDCA products (below) indicated that additional wildfires were active farther to the south in Chile — with notable fires to the west of Curicó (the southernmost METAR site plotted in the imagery), which continued burning into the daytime hours on 04 February.

GOES-16 daytime True Color RGB and Nighttime Microphysics RGB images from the CSPP GeoSphere site revealed dense smoke plumes from the Viña del Mar and Valparaiso area that were transported northward — and clusters of hot fire pixels (darker shades of purple to blue) that persisted well after sunset — on 02 February (above) and 03 February (below).

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The four-panel animation below covers the initiation of the fires. The fire temperature RGB shows that most of the surface is red, because surface temperatures are very warm: Land Surface Temperatures from GOES-16 show values exceeding 120^o F during the warmest part of the day, cooling to the mid-90s by 2300 UTC. Initiation of the fires shows up as a brighter red point that quickly turns more yellow and whitish as the fires intensify.

===== 05 February Update =====

A 30-meter resolution Landsat-9 Natural Color RGB image at 1440 UTC on 05 February (above) revealed the burn scar from the wildfire complex that destroyed portions of Viña de Mar and Quilpué.

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GOES-18 (GOES-West) and GOES-16 (GOES-East) True Color RGB images from the CSPP GeoSphere site (above) showed hazy plumes of blowing dust lofted by Tehuano gap winds that emerged from the south coast of Mexico — which spread out across the Gulf of Tehuantepec and the adjacent waters of the Pacific Ocean on 27-30 January 2024 (long, narrow rope clouds delineated portions of the gap wind boundary on 28/29/30 January). Most Tehuantepec Wind events tend to last 24 or perhaps 48 hours — so the 3+ day duration of this particular episode was fairly unusual.

GOES-16 “Red” Visible (0.64 µm) images on 30 January (below) included plots of Metop ASCAT winds (with several red Gale Force wind vectors over the Gulf of Tehuantepec) and plots of surface/buoy/ship reports (with notable ship reports of 35 knot winds at 1400 UTC, and Blowing Dust at 1800 UTC). The cold front responsible for this Tehuano wind event moved rapidly southward across the western Gulf of Mexico and entered the Isthmus of Tehuantepec on 27 January (surface analyses) — and reached its southernmost position across southern Nicaragua on 30 January.

GOES-16 “Red” Visible (0.64 µm) images with an overlay of the Dust Detection derived product at 4 different times from 28-30 January (below) showed examples of Medium Confidence dust detection.

Surface wind speeds derived using Metop-B/C ASCAT and GCOM-W1 AMSR2 data (source) showed portions of the Tehuano wind field as it spread out across the Gulf of Tehuantepec and the Pacific Ocean during 28-30 January (below).

As a result of the strong gap wind flow, Significant Wave Heights derived from Jason-3 on 29 January and Sentinel-3A on 30 January (below) reached maximum values of 13-17 ft.

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10-minute Full Disk scan GOES-18 (GOES-West) Air Mass RGB images (above) showed a compact polar low as it migrated southeastward across the Bering Sea (not far south of the sea ice edge: surface analyses) on 27-28 January 2024. As the polar low moved through the Pribilof Islands on 28 January, St Paul Island (PASN) experienced a peak wind gust of 59 knots (68 mph) at 1216 UTC, and St. George (PAPB) had a peak wind gust of 47 knots (54 mph) at 1445 UTC. In addition, at PASN the visibility was briefly restricted to 1/4 mile with heavy snow as the polar low passed through the Pribilofs (plot of surface report data).

RCM-2 Synthetic Aperture Radar (SAR) surface wind speed imagery (source) at 1814 UTC on 27 January (below) depicted a compact semi-circular region of wind speeds around 50 knots (darkest shades of red) near or just west of the center of the polar low, as it was still located over the western Bering Sea (1810 UTC Air Mass RGB image | 1800 UTC surface analysis). Smaller pockets of orange-to-red along the trailing cold front were more likely a result of SAR signal backscatter — due to glaciation of convective clouds along the frontal boundary — rather than an indication of higher surface wind speeds.

During the relatively brief ~4 hour period of daylight hours on 27 January, GOES-18 Day Cloud Type RGB images (below) displayed a signature near the core of the polar low — and along its trailing cold front — suggestive of glaciating shallow convective clouds (darker shades of green). With the strong offshore flow of very cold arctic air from Southwest Alaska, widespread parallel cloud streets were evident across the open water of the Bering Sea (likely causing areas of ocean effect snow).

A sequence of 3 Suomi-NPP VIIRS Day/Night Band images (below) provided further evidence of shallow convective cloud banding near the low center and along the cold front.

Suomi-NPP VIIRS Day/Night Band images at 1223 UTC and 1403 UTC on 28 January (below) showed 2 nighttime views of the polar low as it was in the vicinity of the Pribilof Islands.

?Check out this stunning example of a #polar #low forming along the ice edge, behind the arctic front. These lows are classified based on how they form. But they tend to be small (mesoscale), but can be very strong. #akwx @uafgina pic.twitter.com/SsREA9oatQ

— NWS Fairbanks (@NWSFairbanks) January 27, 2024

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