Airmass RGB imagery every hour from 1000 UTC on 14 December through 1900 UTC on 15 December, below, overlain on top of GOES-18 Level 2 Total Preciptable Water, show strong convection in between Tutuila and the Manu’a islands of American Samoa mostly ending after 0000 UTC on 15 December, but the airmass given the green signal in the RGB (click here for help in interpreting the airmass RGB) remains tropical.

GsMap estimates of 24-h rainfall, below, show that the heaviest rains — a maximum of 150+ mm — occurred in between Tutuila and the Manu’a Islands, but >2″ rains occurred over Tutuila, Ofu and Olosega. Rock slides were reported over western Tutuila (click here for the Local Storm Report).

MIMIC Total Precipitable Water fields, below, (from here) for the 24 hours ending 1900 UTC on 15 December, show abundant moisture over all of Samoa with more arriving from the east. Accordingly, Flood Watches (and a small craft advisory) continue through Saturday.

The MetopB Advanced Scatterometer (ASCAT) winds, below, show the strong winds associated with convection south of the Manu’a Islands at 2100 UTC on 14 December. Note also the cyclonic circulation to the north of Samoa.

GOES-18 Visible Imagery, below, from this site, show strong convection to the north of Samoa at 2000 UTC. Given the moisture shown in both the MIMIC TPW and GOES-18 TPW fields that surround the Samoan islands, however, isolated heavy showers may occur at any time throughout Samoa, and showers were occurring over Tutuila at 2100 UTC on 15th. The small line of clouds responsible is apparent in the imagery below towards the end of the animation.

_______________________

More heavy rain occurred across parts of American Samoa on 16 December, as shown in this blog post.

View only this post Read Less

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.

View only this post Read Less

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:

View only this post Read Less

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,

View only this post Read Less