GOES-13 10.7 µm IR images

TROPICAL STORM IRENE SPECIAL DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092011
700 PM AST SAT AUG 20 2011

AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING THE TROPICAL WAVE EAST OF THE LESSER ANTILLES FOUND A SMALL LOW-LEVEL CIRCULATION CENTER JUST SOUTHWEST OF A LARGE CONVECTIVE BURST AND A MINIMUM PRESSURE OF ABOUT 1006 MB. THE PLANE ALSO MEASURED A MAXIMUM WIND OF 53 KT AT 1400 FT AND BELIEVABLE WINDS OF ABOUT 45 KT FROM THE SFMR. THUS ADVISORIES ARE BEING INITIATED ON TROPICAL STORM IRENE WITH AN INITIAL INTENSITY OF 45 KT.

GOES-13 10.7 µm IR images from the CIMSS Tropical Cyclones site (above) showed the large convective burst, along with the location and initial NHC forecast track of the center of Irene.

Within the large convective burst feature, GOES-13 IR / Water Vapor brightness temperature difference product images (below) displayed negative values (green to yellow to red color enhancement) indicative of intense overshooting tops — a signature that is favorable for continued intensification.

GOES-13 IR / Water Vapor brightness temperature difference images

===== 21 August Update =====

The GOES-13 satellite was placed into Rapid Scan Operations (RSO) beginning at 10:15 UTC on 21 August (providing images as frequently as every 5-10 minutes), to monitor Tropical Storm Irene as it approached Puerto Rico. McIDAS images of GOES-13 0.63 µm visible channel data (below; click image to play animation) showed the development of a well-defined cyclonic circulation, as well as a few low-level outflow boundaries propagating outward along the southwestern quadrant of the storm.

GOES-13 0.63 µm visible channel images (click image to play animation)

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GOES-13 0.63 µm visible channel images

A tornado produced EF1 damage and was responsible for one fatality (NWS Green Bay summary) as it moved though the town of Wausaukee in far northeastern Wisconsin during the late afternoon hours on 19 August 2011. This event brought the number of tornado deaths to 550 so far in 2011, making this the 4th deadliest year on record so far in terms of tornado-related fatalities.

McIDAS images of 1-km resolution GOES-13 0.63 µm visible channel data (above) showed the development of the thunderstorm along the Wisconsin/Michigan border region around 18:00 UTC (1:00 pm local time), which then moved southeastward ahead of an advancing cold frontal boundary. The “W” overlaid on the images indicates the location of Wausaukee. Some features to note on the GOES visible imagery include: (1) the formation of a series of northwest-to-southeast oriented boundary layer horizontal convective roll clouds in the vicinity of Iron Mountain (station identifier KIMT), which marked the location of a residual convective outflow boundary from a squall line which moved eastward across the Upper Peninsula of Michigan during the early morning hours on 19 August, (2) subtle storm top shadowing indicating the presence of vigorous overshooting tops, and (3) the development of a well-defined back-sheared storm top anvil along the western edge of the storm toward the end of the animation. A photo of the back-sheared anvil was taken from the Green Bay, Wisconsin area around 00:40 UTC, looking northeast toward the storm (below, courtesy of Peg Zenko).

Photo of back-sheared anvil (courtesy of Peg Zenko)

AWIPS images of 4-km resolution GOES-13 10.7 µm IR channel data (below) showed that cloud top IR brightness temperatures associated with this storm cooled to about -60ºC (darker red color enhancement), but no distinct “enhanced-v” or other severe storm top signatures were apparent.

GOES-13 10.7 µm IR channel images

However, about an hour and 45 minutes before the tornado moved through Wausaukee, a comparison of a 1-km resolution POES AVHRR 10.8 µm IR image with the corresponding 4-km resolution GOES-13 10.7 µm IR image around 20 UTC (below) illustrated the distinct advantage of higher spatial resolution for detecting the presence of colder overshooting cloud tops (-69ºC on POES AVHRR, compared to -57ºC on GOES) as well as important cold/warm thermal couplets (the POES AVHRR image displayed a well-defined cold/warm thermal couplet of -69ºC/-49ºC).

POES AVHRR 10.8 µm IR image + GOES-13 10.7 µm IR image

The GOES-13 sounder Convective Available Potential Energy (CAPE) derived product image at 19:00 UTC (below) revealed that there were pockets of CAPE in the 2300-2900 J/kg range (brighter yellow color enhancement) just ahead of the developing storm, which at that time was centered just west-northwest of Land O Lakes, Wisconsin (station identifier KLNL).

GOES-13 sounder Convective Available Potential Energy (CAPE)

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GOES-14 visible channel image of TD #8

A strong tropical depression has been moving west-northwestward through the Caribbean, and is north of Honduras on August 19th. The visible image loop above, using data from GOES-14 (over the Equator at 105º West Longitude), shows the disturbance at 1330 UTC on August 18th and on August 19th. Some modest increase in organization is discernable, as well as the motion to the west-northwest.

Stereoscopic view of TD #8

Data from GOES-14 and GOES-13 can be used to produce a stereoscopic view of the tropical depression, above. Three dimensions become visible using this technique. This allows the strong thunderstorms near the depression center to pop up out of the screen, and it also facilitates viewing the thin cirrus at the edges of the disturbance.

Data available at the CIMSS Tropical Weather Website shows the tropical depression over very warm water and in an environment of low shear. Despite proximity to land, it is expected to strengthen to Tropical Storm status on the 19th; if it does, it will be named Harvey.

(Update: Harvey achieved tropical storm status at 1800 UTC on 19 August)

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GOES-13 / GOES-14 visible channel image

The Atlantic Tropical Season’s seventh named storm, Gert, was southeast of the island of Bermuda on Monday August 15th on a projected path that keeps it well to the east of Bermuda. The morning full-resolution visible imagery (above) from GOES-13 (left) and GOES-14 (right) show a well-defined Central Dense Overcast through which are penetrating a few overshooting tops. These tops are far more easily visualized with the more oblique viewing angle afforded by GOES-14 (overhead at 105º West Longitude vs. 75º West Longitude for GOES-13). AVHRR Infrared Imagery from NOAA-16 shows brightness temperatures below -75º C with the coldest of the overshoots.

GOES-13 Enhanced Infrared and Observed Shear

Gert is at present in a region of small shear, as shown in the analysis above taken from the CIMSS tropical weather website. However, the projected path is towards higher shear. Strengthening to hurricane status may be difficult because of the increase in shear and because of progressively colder water along the projected path of Gert into the northern Atlantic. There has not yet been a hurricane season in the Atlantic during which none of the first 7 named storms — ‘A’ through ‘G’ — achieved hurricane status. (In 2002, Gustav was the first Hurricane after 6 Tropical Storms).

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