5-minute CONUS sector GOES-16 (GOES-East) Red Visible (0.64 µm) images (above) displayed an intensifying Hurricane Force low pressure system over the western Atlantic Ocean (not far off the North Carolina coast) on 15th November 2024. Note the area of haziness just west-southwest of the center of the surface low — this milky/hazy appearance was due to the enhanced diffuse reflection of sunlight off a very agitated sea surface (where high waves and abundant sea spray were present, caused by a burst of strong surface winds across that particular area).

About an hour after the beginning of the GOES-16 Visible image animation, Metop-C ASCAT Ultra High Resolution surface winds at 1529 UTC (source) depicted a small area of wind speeds greater than 50 knots, just west of the light winds near the center of the low pressure system (below) — and the 1531 UTC GOES-16 image also showed a few GOES-16 Derived Motion Wind vectors with speeds of 51-53 knots just west of the surface low.

GOES-16 Visible images that included plots of GOES-16 Derived Motion Winds (DMW) within the marine boundary layer (Surface-900 hPa) are shown below — which highlighted cloud-tracked DMW speeds of 63-66 knots (72-76 mph) just south of the hazy-appearing areas of rough seas.

The hazy-appearing area of high waves + sea spray was even more apparent in 1-minute Mesoscale Domain Sector GOES-16 True Color images from the CSPP GeoSphere site (below). A few southeastward bursts of cumulus clouds were also seen emanating from the southern edge of the region of dense convective clouds — a potential signature of a sting jet descending toward the sea surface.

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The Night Microphysics RGB animation from the CSPP Geosphere site (direct link to animation) below shows clouds of various heights (and temperatures). For example deep high clouds (likely precipitating) stretch northwest to southeast to the north of the Samoan Island chain. Low clouds are indicated over the three main Samoan islands: Savai’i, Upolu and Tutuila (from west to east), as indicated by the light violet/cyan enhancement over those islands. Given the stationary nature of the enhancement in the RGB, one might imagine the clouds perched atop the higher terrain of those three islands. At the end of the animation, note the north-south cloud band that is moving over Tutuila, the main island of American Samoa, shown in the annotated toggle below. Would you expect rain to fall from that line? You might not; after all, the lines of tropical cumulus south and east of the Samoan Islands do not show the color changes typical in developing cumulus in the Nighttime Microphysics RGB (as discussed here, for example).

GOES-18 GREMLIN fields, below, show persistent rains to the north of the Samoan Islands — especially after 1000 UTC — but no signal with the shallow cloud bands moving eastward to the south of this convective band.

GOES-18 Clear-Sky Total Precipitable Water fields, shown below with Band 13 clean window infrared (10.3 µm) imagery, show the Samoan Islands in an atmosphere rich with moisture (values exceed 1.9″), with a slightly dryer atmosphere to the north and south.

At 1350 UTC, the time at the end of the Night Microphysics RGB shown at the top of the blog post, GOES-18 Cloud Top Heights are between 10000 and 15000 feet (three blue pixels) to the southeast of Tutuila. Values just north of Tutuila are closer to 6000 feet.

What was the stability of the atmosphere between 6000 and 16000 feet at this time? That’s a challenge. The Upper Air site at Pago Pago is launching balloons just once every two days — because of a gas shortage; a launch did occur at 2300 UTC on 12 November and that sounding is shown below.

NOAA-20 overflies American Samoa daily at about the times of the radiosonde launch. Sounding availability at 0120 UTC on 13 November 2024 is shown below. Let’s compare the satellite-derived NOAA-20 NUCAPS sounding to the west of Tutuila and to the west of Tutuila given the observation above. NUCAPS does capture the relatively dry air between 500 and 700 mb, and hints at the inversion above the moist boundary layer.

The western sounding above is considerably dryer than the sounding to the east: 1.54″ of PW vs. 1.92″ (note that the rawinsonde from NSTU had a computed PW of 1.75″. MIMIC TPW fields at 0000 UTC, below, show that strong gradient over the Samoan Islands that is captured in the soundings above. (Here’s an animation that shows the movement of that gradient).

At 1200 UTC, station NSTU/91765 did not launch a balloon. However, NOAA-20 overflew the site and the Sounding Availability plot is shown below. There are 4 NUCAPS soundings that surround Tutuila — to the NW, NE, SE and SW. They are shown below.

The 1200 UTC soundings all have similar Precipitable Waters (around 1.8″; here is the MIMIC TPW at 1200 UTC). Abundant moisture is present. That showers did not develop as over American Samoa reflects a combination of mid-level dry air (seen in the NUCAPS soundings above) and a lack of strong forcing. (My experience forecasting for Pago Pago is full of forecasts that did not verify!). Gridded NUCAPS fields, such as 700-mb Dewpoint Temperature, below, also showed the a tongue of dry air over Samoa.

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Until (and after!) regular sounding launches recur at Pago Pago, continue to look at the NUCAPS soundings, and assess how they are changing from day to day. That will help you determine how upper levels over station 91765 are evolving.

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5-minute PACUS/CONUS sector Upper-level Water Vapor (6.2 µm) images with an overlay of GLM-detected Flash Extent Density from GOES-18 (GOES-West) and GOES-16 (GOES-East) (above) showed the detection of a bolide — which according to the American Meteor Society occurred around 1333 UTC on 13th November 2024.

Since the bright fireball occurred at a high altitude (as a meteor was entering the Earth’s upper atmosphere), there was a notable parallax shift in the GLM-detected signatures (it should be noted that Level 3 GLM gridded products such as Flash Extent Density are not parallax-corrected) — with the apparent location over southwest Alberta as viewed from GOES-18, and over southeast British Columbia as viewed from GOES-16. With both satellites positioned over the Equator, a parallax-induced northward shift in apparent location would also need to be accounted for (GOES-18 parallax correction | GOES-16 parallax correction); this would bring the actual bolide location southward, to a point over far northwestern Montana (the blue fireball trajectory arrow pointing southeastward on the AMS map).

Satellite viewing angle also had a small effect on the GLM Flash Extent Density magnitude (1336 UTC image) — with a peak FED value of 6.0 observed by GOES-18, compared to 4.0 observed by GOES-16. Conversely, the peak Total Optical Energy values were 898.8 fJ observed by GOES-18 compared to 2241.7 fJ observed by GOES-16 (below).

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Day Night Band imagery from the three JPSS Satellites — NOAA-21 (1515 UTC), Suomi NPP (1537 UTC) and NOAA-20 (1602 UTC) show Tropical Storm Man-Yi as it approached the southern Marianas Islands early in the morning on 13 November 2024 (Guam Time). These images were created using CSPP Software and data downloaded at the Direct Broadcast site on Guam. The Deep Convection with the system is close to the surface center. That was not the case 12 hours earlier!

Himiwari-9 visible imagery (Band 3, 0.64 µm), below (from this site), from 0300 – 0510 UTC on 12 November show a low-level swirl of clouds to the northwest of the deepest convection.

Shortwave infrared imagery from Himawari-9 (Band 7, 3.9 µm) shows the low-level circulation separate from the convection until about 1000 UTC. Shortly before that time, convection develops into and persists within the center of the low-level swirl of clouds.

As of 0000 UTC on 13 November, the deepest convection with Man-Yi is passing south of Guam. Winds at the Guam airport are easterly, with gusts to 40 mph. The statement below was issued at 841 AM/13 November Chamorro Standard Time (2241 UTC on 12 November).

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Thanks to Douglas Schumacher, CIMSS, for the Day Night Band imagery from Guam.

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