Sentinel-1A’s overpass over the Gulf of Tehuantepec shortly after 0000 UTC on 13 December, shown above in a toggle with topography, corresponded with the beginning of an event of strong winds (colloquially called a “Tehuantepecker”) cause by funneling of wind through the Chivela Pass in the Sierra Madre mountains. At 0031 UTC, the time of the overpass (Normalized Radar Cross Section fields at that time are here; note also the wind field on 17 December!), winds are near 40 knots over the Pacific Ocean, and the wind structure has a noticeable banded structure. This NOAA/STAR website also allows a user to view the Sentinel-1A NRCS fields, and the winds.

Advanced Scatterometer (ASCAT) winds over the same region similarly outline very strong winds from this event, over two days, with winds up to 40 knots. ASCAT horizontal resolution is insufficient to capture the different bands of strongest winds as seen in the SAR data.

Visible imagery from both 13 December and 14 December, shown below, show the characteristic clearing down wind of the Sierra Madre mountains as air descends (and dries).

Other notable Tehuano wind events have been documented in these blog posts.

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Coronal holes typically result in high-speed solar wind streaming outward, and in this case, directly towards Earth. This scenario sometimes prompts NOAA Space Weather to issue a Geomagnetic Storm Watch, but almost always results in vibrant Aurora Borealis activity when the solar wind reaches Earth. This was the case in the early hours on the 14^th of December, revealed by the VIIRS Day Night Band sensor flying on NOAA’s polar-orbiting satellites. 

The following 3 images were acquired by the NOAA-21 satellite:

These 3 images were acquired by the NOAA-20 satellite:

Three images were also acquired by the Suomi-NPP satellite:

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Target Sector (2.5-minute interval) JMA Himawari-9 AHI Red Visible (0.64 µm) and Clean Infrared Window (10.4 µm) images (above) showed the brief development of a ragged eye with Cyclone Jasper as the storm approached the coast of Far North Queensland, Australia — prior to it making landfall north of Cairns around 1200 UTC on 13 December 2023.

In Synthetic Aperture Radar (SAR) wind speed images from RCM-3 at 1956 UTC on 12 December and 0854 UTC on 13 December (source), a swath of higher speeds (having maxima of 65.78 knots and 49.62 knots, respectively) was seen within the southern semicircle of the eyewall (below).

A GCOM-W1 AMSR2 Microwave (85 GHz) image at 1554 UTC on 13 December (below) also displayed higher reflectivity within the southern eyewall, moving inland near and just north of Cairn surface observation site.

Himawari-9 Infrared Window (11.2 µm) images from the CIMSS Tropical Cyclones site (below) showed that Jasper was moving through an environment of low deep-layer wind shear — which, in addition to its motion across modestly-warm water (SST | OHC) favored some intensification. In fact, Jasper did intensify to 60 knots at 0600 UTC on 13 December (SATCON), about 6 hours prior to landfall,

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National Weather Service Pago Pago Facebook posts on 11 December describe an atmosphere primed for heavy rain and lightning, the latter Facebook also shown below. Band 13 animation, above, shows persistent deep convection over the Samoan Islands. The convection develops and drifts southward.

MIMIC Total Precipitable Water over the south Pacific shows moist air over Samoa being drawn poleward in an atmospheric river. (Cyclone Jasper (see this also) along the northeast coast of Australia is also apparent).

ASCAT Scatterometry data from Metop-B, below (source), shows strong surface convergence over the Samoan Islands.

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Lightning events on 12 December are shown below from this link. In this case, GOES-18 Flash Extent Density field are overlain on GeoColor imagery. Abundant lightning is occurring north and south of the Samoan Islands. An Airmass RGB animation from the same website (here), shows the persistent southward motion of moist tropical air over the Samoan Islands.

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