August 31st, 2010
GOES-13 6.5 µm "water vapor channel" images
Evidence of a large region of mid-tropospheric dry air on AWIPS images of GOES-13 6.5 µm “water vapor channel” data (above; also available as a QuickTime movie) in tandem with an increase in southwesterly deep layer wind shear was helping to erode the upper level cloud canopy over the western portion of Category 4 Hurricane Earl — this allowed a well defined low-level outflow boundary to be seen on McIDAS images of GOES-13 0.63 µm visible channel data (below; also available as a QuickTime movie) on 31 August 2010.
It is also interesting to note the westward-propagating “shock waves” that were emanating from Hurricane Earl, which could be seen on the water vapor imagery in the dry region (denoted by the predominantly yellow color enhancement) over the western Atlantic Ocean.
GOES-13 0.63 µm visible channel images
A comparison of AWIPS images of the POES AVHRR 0.63 µm visible and 10.8 µm IR channel data (below) seemed to support the fact that this was indeed a low-level feature, with the narrow cloud band of the outflow boundary feature exhibiting fairly warm IR brightness temperatures of 0º to +5º C.
POES AVHRR 0.63 µm visible and 10.8 µm IR images
The POES AVHRR Cloud Top Height (CTH) product (below) gave maximum CTH values of 3-4 km (red color enhancement) for the outflow boundary feature — maximum CTH values near the center of Hurricane Earl were around 16 km (cyan color enhancement).
POES AVHRR 10.8 µm IR image and Cloud Top Height product
Further confirmation that this was a low-level feature was provided by an examination of the AVHRR Cloud Type product (below), which indicated that the narrow outflow boundary cloud band was composed of water droplets (cyan color enhancement).
POES AVHRR 0.63 µm visible image and Cloud Type product
August 30th, 2010
GOES-15 imagery shows the steady development of a distinct eye feature with Earl as the storm slowly moves away from the Leeward Islands. The 11 AM 30 August National Hurricane Center discussion notes peak sustained winds of 105 knots; Earl is a category 3 storm that is moving over warm water in an environment of low shear. Strengthening is forecast. Interests along the east coast of the United States and Canada should monitor the evolution of this system.
The infrared imagery shows cold cloud tops surrounding much, but not all, of the developing eye. Coldest cloud top brightness temperatures — the light purples within the greys — are values around -80 C.
In the loop above, GOES-13 and GOES-15 imagery are combined to give a stereoscopic view of the storm, allowing a three-dimensional perspective.
GOES-13 0.63 µm visible images
A closer view of the eye of Hurricane Earl is shown using GOES-13 0.63 µm visible images (above; also available as a QuickTime movie) — the satellite was in Rapid Scan Operations (RSO), providing images as frequently as every 5-10 minutes. Near the end of the time of the visible image animation, a comparison of 1-km resolution NOAA-15 AVHRR and 4-km resolution GOES-13 IR images (below) revealed that the coldest cloud top IR brightness temperatures were located in the northeastern quadrant of the eyewall region (as cold as -86º C on the NOAA-15 image, and -80º C on the GOES-13 image). By this time, Hurricane Earl had reached Category 4 intensity on the Saffir-Simpson Hurricane Scale.
NOAA-15 10.8 µm IR and GOES-13 10.7 µm IR images
August 30th, 2010
1-km resolution MODIS + 4-km resolution GOES-13 fog/stratus product images
During the pre-dawn hours of 30 August 2010, AWIPS images of the 1-km resolution MODIS and the 4-km resolution GOES-13 fog/stratus product at around 07 UTC (above) demonstrated the importance of spatial resolution in displaying the location of narrow fingers of river valley fog features across parts of the northeastern US.
About 2.5 hours later, a similar comparison between the 1-km resolution AVHRR and the 4-km resolution GOES-13 fog/stratus products (below) showed that the GOES-13 image was overwhelmed with a widespread “false fog/stratus signal” problem, which made the AVHRR image all the more valuable at that particular time.
1-km resolution AVHRR + 4-km resolution GOES-13 fog/stratus product images