August 28 2015 is the 10-year anniversary of Hurricane Katrina achieving Category 5 status (on the Saffir-Simpson Scale) in the central Gulf of Mexico. The mp4 animation above (available here as a 490 megabyte animated gif, and on YouTube) shows the evolution of Katrina from a thunderstorm cluster in the Bahamas to a weak hurricane off the west coast of Florida to a Category 5 Hurricane in the central Gulf before weakening somewhat at landfall along the central Gulf coast. (The archive of National Hurricane Center advisories is here. The post-storm write-up is here.)

GOES-12 was in service as GOES-East during Katrina’s life, and as a GOES I-M satellite it lacked batteries to allow imaging through eclipse, which occurs as the satellite passes through the Earth’s shadow (solar panels in shadow do not provide power) in the weeks surrounding the Equinoxes. The toggle above from 28 August 2005 shows the last pre-eclipse image (0402 UTC) and the first post-eclipse image (0615 UTC); considerable organization of the storm has occurred in those two hours! GOES satellites from GOES-13 on have sufficient battery capacity to provide imagery through eclipse periods (for example, see this GOES-13 vs GOES-12 comparison during the landfall of Hurricane Ike along the Texas coast in 2008).

Katrina was featured in the CIMSS GOES Gallery back in 2005 (Link).

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A large Mesoscale Convective System (MCS) developed over western South Dakota late in the day on 26 August 2015, moving eastward across the state and producing wind gusts as high as 79 mph (SPC storm reports). A nighttime comparison of Suomi NPP VIIRS Infrared (11.45 µm) and Day/Night Band (0.7 µm) images at 0842 UTC (above) showed the large cloud shield with cloud-top IR brightness temperatures as cold as -74º C at the central cluster of overshooting tops; bright white pixels on the Day/Night Band image were portions of the cloud illuminated by intense lightning activity. Various types of waves were also seen in the VIIRS imagery: (1) concentric gravity waves propagating outward from the central cluster of overshooting tops, (2) transverse banding emanating radially outward in portions of the northern semicircle of the MCS, and (3) a large arc of waves moving westward away from the back edge of the storm.

Regarding the large arc of waves along the back edge of the MCS, GOES-13 (GOES-East) water vapor (6.5 µm) images (below; click image to play animation) revealed a signal of strong subsidence (warming/drying, darker blue color enhancement) as the westward-expanding cloud mass was acting as an obstacle to the prevailing westerly winds coming from Wyoming and Montana.

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GOES-13 Infrared Imagery (above) for the 24 hours ending 1415 UTC on 26 August 2015 show Tropical Storm Erika approaching the Leeward Islands of the eastern Caribbean. A general increase in convection in the 24 hours shown is obvious. Visible imagery (below) from the morning of 26 August shows some overshooting tops within the central dense overcast (CDO) covering the low-level circulation. A plot of the number of overshooting tops in Erika is here (taken from this webpage). Outward-propagating gravity waves can also be seen at the top of the CDO.

Surface winds as observed by the Metop ASCAT Scatterometer early on 26 August (0056 UTC), below, show a modest circulation with winds that are mostly below tropical storm force (Added: The 1411 UTC image, bottom, shows some tropical-storm force wind flags). Dry Saharan Air Layer air should not limit intensification of Erika, but wind shear just north and west of the storm is strong (SAL and Wind Shear imagery taken from the CIMSS Tropical Cyclones site).

For the most recent forecasts on Erika’s future, see the National Hurricane Center website.

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Typhoon Atsani (which reached Category 5 intensity in the West Pacific Ocean on 19 August 2015) began to transition to a strong post-tropical storm on 25 August. JMA Himawari-8 water vapor (6.2 µm) images (above; click to play MP4 animation) showed the transformation as warm/dry air (yellow to red color enhancement) began to wrap into the western and southern portion of the storm. The animation is also available as a very large QuickTime movie (76 Mbytes) or an animated GIF (110 Mbytes).

Surface analyses from the Ocean Prediction Center (below; click to play animation) indicated that the post-tropical storm deepened to a minimum central pressure of 957 hPa at 12 UTC on 25 August, and was producing hurricane-force winds until 00 UTC on 26 August.

#Atsani transitions from typhoon into powerful HF post-tropical low impressive, short video: https://t.co/uMfMPOBh2M pic.twitter.com/InXpkA6B4Y

— NWS OPC (@NWSOPC) August 25, 2015

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