The GOES-15 imagery includes the northern fringe of the Intertropical Convergence Zone, and the active eastern Pacific Hurricane season is apparent, including several storms that have threatened the state of Hawai’i. The atypically strong August storm that hit the Pacific Northwest is also apparent at the end of the animations.]]>
An animation of GOES-15 (GOES-West) Infrared (10.7 µm) images (below; click image to play animation) showed the evolution of these 3 tropical cyclones during the 29-30 August period.The MIMIC Total Precipitable Water product (below; click image to play animation) indicated that all 3 storms were easily able to tap abundant moisture from the Intertropical Convergence Zone (ITCZ). A longer animation of the MIMIC TPW product covering the period 21 August to 01 September is shown below. ]]>
A comparison of 1-km resolution POES AVHRR Visible (0.86 µm) and Infrared (12.0 µm) images at 2330 UTC or 6:30 PM local time (below) showed the developing convective storms in greater detail. The coldest cloud-top IR brightness temperature was -73º C with the westernmost cluster of thunderstorms.A closer view of the GOES-13 Infrared images with METAR surface reports is shown below. Note that Sioux Falls had a peak wind gust of 32 knots (37 mph). The Blended Total Precipitable Water (TPW) Percent of Normal product (below; click to play animation) showed TPW values as high as 199% of normal just to the north-northeast of Sioux Falls at 0442 UTC (11:42 PM local time).
Check out the rainfall on the west side of Sioux Falls. Almost an inch of rain fell in 10 minutes! pic.twitter.com/OYavFY67pp
— NWS Sioux Falls (@NWSSiouxFalls) August 28, 2015
How unprecedented was the rain? At a SDSU automated rain gauge at Sertoma Park, it measured 2.73″ of rain within 25 minutes! Wow! — NWS Sioux Falls (@NWSSiouxFalls) August 28, 2015
At the same gauge at Sertoma Park, it recorded 0.71″ of rain within 5 minutes! That’s a lot of water!
— NWS Sioux Falls (@NWSSiouxFalls) August 28, 2015
Updated precip total map – thanks to NWS FSD for additional data. #sdwx #siouxfalls pic.twitter.com/fc9qHqZZ2y — Dennis Todey (@sdclimatologist) August 28, 2015
Wondering how much rain you received last night? Here is a map of rainfall reports we received. pic.twitter.com/rqUF6AVYdf
— NWS Sioux Falls (@NWSSiouxFalls) August 29, 2015
Katrina was featured in the CIMSS GOES Gallery back in 2005 (Link).]]>
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.]]>
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
The first tropical storm of the season in the eastern Atlantic (Ana, Bill and Claudette all formed over the western Atlantic) has formed from a cluster of thunderstorms that emerged from Africa. The multi-day animation, above, from GOES-13, shows the steady progress of the disorganized system across the eastern Atlantic basin. Visible Imagery from GOES-13 and Meteosat-10, below, from the morning of 19 August, show the system near 40 W. The cyclonic curvature to the clouds is apparent; identification of the center in infrared imagery, below, is more difficult. Convection to the east of Danny has colder cloud top temperatures.
ASCAT winds from 0100 UTC on 19 August 2015 (above) show a compact circulation center with winds of 40 knots just north of 10 N and east of 40 W.
A persistent impediment to Tropical Cyclone initiation in the eastern Atlantic this year has been widespread Saharan Air Layer dust. The one-day animation, above (taken from this website), shows the SAL persists over the Atlantic; Danny has formed just to the south. Wind shear over Danny at present is weak (see below [source]), and slow strenghtening is expected as Danny approaches the Caribbean.
The Discussion from the National Hurricane Center at 0900 UTC on 19 August included this phrase: “The center is difficult to locate on infrared images,…” The Day Night Band from VIIRS on Suomi NPP can sometimes be used to locate low-level circulation centers of tropical systems. This relies on the presence of moonlight, however, and when Suomi NPP overflew Danny just before 0500 UTC on 19 August, the moon was below the horizon. Thus, the Day Night Band, below (Courtesy of William Straka) gave very little information.
More information on Danny is available at the CIMSS Tropical Weather Website. Consult the National Hurricane Center for the latest updates and official forecasts.]]>