Hurricane Ophelia over the central Atlantic

September 30th, 2011
GOES-13 Visible images (click image to play animation)

GOES-13 Visible images (click image to play animation)

Hurricane Ophelia, the fourth hurricane of the north Atlantic tropical season, is pictured above near peak intensity as it moves over the open waters of the Atlantic Ocean, northeast of Hispaniola (which island is visible in the southwest corner of the image loop). The hurricane displays a circular central dense overcast region around a eye in which one might infer the presence of small-scale vortices. Several factors argue for weakening with Ophelia. Note in the animation the motion of the cirrus clouds entering the frame from the west. These high-level winds suggest an increase the shear over Ophelia, and in fact the convective distribution around the storm shows an asymmetry with more convection east of the center. Further, Ophelia’s projected track takes it across a region of ocean that is cooler following the passage of major Hurricane Katia earlier in September. This cool wake limits the energy available to subsequent storms like Ophelia. This loop toggles between images retrieved from the CIMSS Tropical Weather website, showing an enhanced infrared image and a mapping of the sea surface temperatures over the Atlantic in which the wake of Katia is plain. Observations from AVHRR confirm the existence of the cooler SSTs ahead of Ophelia.

The vigor of the convection within a hurricane can be measured by the number of overshooting tops within the circulation. This plot, for example, shows a weakening in Katia as the number of overshooting tops dropped on 2 September. Overshooting tops can be inferred by differencing the 10.7 µm and 6.5 µm channels on the GOES imager. This animation shows only occasional evidence of overshooting tops. Visible imagery from GOES-15 shows evidence of a few overshoots possibly north of the center, and in a spiral band east of the center. A very oblique view from GOES-11 suggests a similar distribution to the overshoots, but also shows a mostly smooth cirrus canopy above the hurricane. The number of overshoots should decrease as Ophelia moves over the cooler waters to its north.

Added: This POES AVHRR Infrared image, showing half of the storm, shows cloud tops as cold as -77 C, but little in the way of overshooting tops. A comparison of this same POES AVHRR IR image (viewed using McIDAS)  with the corresponding POES AVHRR visible image (below) nicely shows the curved convective band that was wrapping around they eye of Hurricane Ophelia.

POES AVHRR 10.8 µm IR and 0.63 µm visible channel images

POES AVHRR 10.8 µm IR and 0.63 µm visible channel images

Persistent cut-off low over the north-central US

September 27th, 2011
GOES-15 6.5 µm water vapor images (click image to play animation)

GOES-15 6.5 µm water vapor images (click image to play animation)

McIDAS images of GOES-15 6.5 µm water vapor channel data (above; click image to play animation) showed the changing signature of a persistent upper level cut-off low lingering over the north-central US during the 23 September27 September 2011 period. As the system lingered over the region, it produced widespread wind gusts in the 30-40 mph range (with a peak wind gust of 46 mph at Green Bay, Wisconsin), and rainfall totals of 4-5 inches at some locations in northern Illinois.

AWIPS images of the hourly GOES sounder Total Column Ozone product on 25 September - 26 September (below; click image to play animation) revealed a distinct elevated ozone signature (300-400 Dobson Units, green to red color enhancement), which indicated that the height of the tropopause was lower in the vicinity of the cut-off low.

 

GOES sounder Total Column Ozone product (click image to play animation)

GOES sounder Total Column Ozone product (click image to play animation)

One notable impact associated with this cut-off low included thunderstorms along the Lake Michigan shoreline that produced a number of waterspouts that were seen from Milwaukee to Chicago. A comparison of MODIS 0.65 µm visible channel and 11.0 µm IR window channel image at 17:28 UTC (12:28 pm local time) on 24 September (below) showed one of the storms that exhibited cloud top IR brightness temperatures colder than -40ºC (blue color enhancement), along with a number of cloud to ground lightning strikes as it moved inland.

MODIS 0.65 µm visible channel and 11.0 µm IR window channel images

MODIS 0.65 µm visible channel and 11.0 µm IR window channel images

Another impact of this cut-off low included a number of pilot reports of light to moderate turbulence over the central and southern Great Plains region. A well-defined bloom of cirrus clouds developed within a zone of high 400-200 hPa layer wind shear, as seen on 4-km resolution GOES-13 6.5 µm water vapor channel images with overlays of CRAS model fields (below; click image to play animation).

GOES-13 6.5 µm water vapor images + turbulence reports + CRAS layer winds and shear (click image to play animation)

GOES-13 6.5 µm water vapor images + turbulence reports + CRAS layer winds and shear (click image to play animation)

Better detail of the banded structure of the cirrus cloud features within the high-shear deformation zone can be seen on a 1-km resolution MODIS 6.7 µm water vapor image (below). Note the pilot report of light to moderate turbulence during the entire flight from Denver (DEN) to Kansas City (MCI).

MODIS 6.7 µm water vapor image + pilot reports of turbulence

MODIS 6.7 µm water vapor image + pilot reports of turbulence

A sequence of 1-km resolution MODIS 6.7 µm water vapor channel images on 26 September (below) showed some very intricate dry air and moisture structures within the cut-off low during that particular day.

MODIS 6.7 µm water vapor channel images

MODIS 6.7 µm water vapor channel images

In a comparison of MODIS 0.65 µm visible channel and MODIS 6.7 µm water vapor channel images (below), note how much more structure is seen in the water vapor image — even in areas that are cloud-free in the visible image. This allows a number of water vapor features and gradients to be tracked using 3 consecutive GOES water vapor images, to produce MADIS high-altitude atmospheric motion vectors (AMVs) that can provide important wind direction and wind speed data. An AMV with a wind speed of 130 knots (at 300 hPa) was seen in the dry slot over southern Missouri.

MODIS 0.65 µm visible image + MODIS 6.7 µm water vapor image + MADIS satellite winds

MODIS 0.65 µm visible image + MODIS 6.7 µm water vapor image + MADIS satellite winds

Autumn tree colors, and a large fire burn scar in northeastern Minnesota

September 26th, 2011
MODIS true color and false color Red/Green/Blue (RGB) images

MODIS true color and false color Red/Green/Blue (RGB) images

A comparison of 250-meter resolution MODIS true color and false color Red/Green/Blue (RGB) images from the SSEC MODIS Today site (above) showed a few interesting features across northeastern Minnesota on 26 September 2011: (1) on the true color image, the appearance of the light orange signature of Autumn tree colors just inland along parts of the Lake Superior shoreline (in stark contrast to the bright white taconite tailings ponds just west/northwest of Silver Bay), and (2) on the false color image, the bright red burn scar from the recent Pagami Creek wildfire that had burned over 93,000 acres (since being started by lightning on 18 August) and was still only 53% contained on this day.

Hurricane Hilary

September 23rd, 2011
GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images (click image to play animation)

GOES-15 0.63 µm visible channel images  (above; click image to play animation) showed the rather small but very distinct eye of Category 4 Hurricane Hilary in the Eastern North Pacific Ocean on 23 September 2011. GOES-15 (the newest in the series of GOES N/O/P satellites, launched and tested in 2010) is scheduled to replace GOES-11 as the operational GOES-West satellite in December 2011.

During this same time period on 23 September, the GOES-11 satellite was placed into Super Rapid Scan Operations (SRSO) mode, providing bursts of data at 1-minute intervals. Magnified versions of GOES-11 0.65 µm visible channel images (below; click image to play animation; also available as a QuickTime movie) revealed that at times there were multiple mesovortices within the eye of Hurricane Hilary. Larger-scale (zoomed-out) views of GOES-11 SRSO Water Vapor, Visible, and IR channel images are available from CIRA/RAMMB.

GOES-11 0.65 µm visible channel SRSO images (click image to play animation)

GOES-11 0.65 µm visible channel SRSO images (click image to play animation)