Satellite imagery and multiple earthquakes near American Samoa

August 25th, 2022 |
False Color imagery over the American Samoa sector, 1610 UTC on 25 August 2022 (Click to enlarge)

Seismic activity has been ongoing in August 2022 beneath the island of Ta’u to the east of American Samoa. (USGS has published a variety of information on this swarm of Earthquakes: link 1; link 2; link 3); See also these two recorded Facebook Live presentations from the NWS WSO office in Pago Pago: (August 22nd and August 17th). Volcano updates fro Ta’u can also be viewed here.

The Volcanic Ash Advisory Center (VAAC) that has responsibility for this region of the south Pacific is Wellington NZ. Click here for a pdf that shows all VAAC boundaries.

Should an eruption occur (NOTE: An eruption is not expected in the near term!), what kind of satellite information will be useful? The Volcanic Cloud Monitoring website (link) from CIMSS includes imagery over various sectors on Earth, sorted by VAAC. For American Samoa, and adjacent regions, Choose ‘Satellite Imagery’ and under the ‘Sector’ menu, and then choose, under the Wellington VAAC subsection, ‘American Samoa (750 m)’ Both GOES-17 / GOES-18 and Himawari view the region, but GOES-17/GOES-18 sub-satellite points are closer to American Samoa and will provide better resolution views. (NOAA-20 and Suomi-NPP as polar orbiters will provide the highest spatial resolution data, but have poor temporal resolution). You can choose various image types at the website: quantitative estimates of Ash Loading, Ash Height, Ash Loading, Ash Reflectivity, Single-channel Brightness Temperatures (or Reflectivity), and various Red/Green/Blue composites. Note that this website has an extensive explanatory section (under the ‘Tutorials’ tab) to help you understand what you’re seeing in the imagery. The GOES-18 false-color image red/green/blue image, above, is the from the website. An eruption is not occurring, nor detected, in the image.

Various websites also allow views of Satellite Imagery over the region. For example, the CSPP Geosphere site includes True-Color imagery (day) and Night time Microphysics (night) by default, but also allows a user to view single channels. (Direct link, see an example below) There is also a NOAA/NESDIS site that includes some RGBs and each of the individual bands; the CIRA Slider also includes imagery over the south Pacific.

Night Microphysics RGB near American Samoa, 1700 UTC on 25 August 2022 (Click to enlarge)

Wind direction will be important if an eruption occurs (this is at present unlikely!!) to know as that will control the dispersion of any gases. The website will provide this with this link.

This blog entry is meant to be a resource should an eruption occur. (Note: that is not expected!) For more information, please refer to the USGS website, and the American Samoa Facebook page.

30th anniversary of the Florida landfall of Hurricane Andrew

August 24th, 2022 |

GOES-7 Infrared (11.35 um) images [click to play animated GIF | MP4]

GOES-7 Infrared (11.35 um) images (above) showed Hurricane Andrew making landfall along the southeast coast of Florida — as a Category 5 storm — around 0831 UTC  on 24 August 1992. At that time, the coldest cloud-top infrared brightness temperatures of the eyewall region were around -75ºC. These images were created using archived data from SSEC Satellite Data Services.

More information on Andrew can be found in this video produced by NWS Miami for the 25th anniversary of the storm.

Monthly Averages of GOES-17 Band 13 Brightness Temperatures for 2021

August 23rd, 2022 |

Access to SSEC’s Data Center allows for some serious “data crunching” with the full record of GOES-17 ABI data. In Figure 1 below, GOES-17 Band 13 Full Disk brightness temperatures have been averaged for each month in 2021. These fields of averaged brightness temperature are useful for assisting forecasters in knowing what can be expected from satellite retrievals on monthly timescales, especially in remote Pacific regions where forecasters are heavily reliant on satellite data.

Figure 1. An animation of monthly mean GOES-17 Band 13 Full Disk brightness temperatures for 2021. [Click to open in new tab.]

2021 was a typical La Nina year, which is associated with dry weather in the Southwest United States. A strong surface heat signal can be seen in that region from April – September.

May – October experiences cooler temperatures in the East Pacific near Mexico and Central America. This may be associated with the 2021 Pacific Hurricane season.

Figure 2 is the same animation for tropical latitudes only. In all months, the ITCZ band is visible. It can be recognized as a band of cooler brightness temperatures (green-teal color) that sits slightly north of the equator. If you look closely, the ITCZ seems to undergo a slight northward migration as the year progresses. This northward shift is more noticeable in the transitions from April to May and from September to October.

Figure 2. An animation of tropical monthly mean GOES-17 Band 13 brightness temperatures for 2021. [Click to open in new tab.]

Heavy rainfall and flash flooding across North Texas

August 22nd, 2022 |

GOES-16 Visible/Infrared Sandwich RGB images, with hourly surface precipitation amounts plotted in white [click to play animated GIF | MP4]

1-minute Mesoscale Domain Sector GOES-16 (GOES-East) Visible/Infrared Sandwich RGB images from 1300-1800 UTC (above) included plots of 1-hour surface precipitation amounts — and showed clusters of thunderstorms moving across North Texas and the greater Dallas/Fort Worth area early in the day on 22 August 2022. These storms were focused along a quasi-stationary surface front that was draped across the region; heavy rainfall during this 5-hour period caused additional flash flooding in locations that had already received substantial precipitation within the previous 24 hours.

A GOES-16 Visible/Infrared Sandwich RGB image at 1410 UTC (below) displayed cursor readouts of the 3 RGB components along with the available Level 2 Derived Products — cloud-top infrared brightness temperatures were colder than -80ºC, Cloud-Top Heights were greater than 54,000 feet and Rainfall Rates were nearly 3.7 inches per hour just south of Terrell, Texas. The Dallas/Fort Worth airport received a record 3.01 inches of rain in 1 hour (tweet).

GOES-16 Visible/Infrared Sandwich RGB image at 1410 UTC, with cursor readouts of RGB components and Level 2 Derived Products [click to enlarge]

Hourly MIMIC Total Precipitable Water images viewed using RealEarth (below) depicted TPW values in the 60-70 mm (2.4-2.8 inches) range, with a peak value of 78 mm (3.1 inches). The 22 August / 00 UTC rawinsonde report from Fort Worth had a TPW value of 2.34 inches, which was a record maximum value for that date/time.

MIMIC Total Precipitable Water product [click to play animated GIF]

Additional satellite imagery and information about this event can be found on the Satellite Liaison Blog