Hurricane Earl produces a low-level outflow boundary

August 31st, 2010
GOES-13 6.5 µm "water vapor channel" images

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

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

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

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

POES AVHRR 0.63 µm visible image and Cloud Type product

Hurricane Earl develops an eye

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

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

NOAA-15 10.8 µm IR and GOES-13 10.7 µm IR images

Locating river valley fog features: the importance of spatial resolution

August 30th, 2010
1-km resolution MODIS + 4-km resolution GOES-13 fog/stratus product images

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

1-km resolution AVHRR + 4-km resolution GOES-13 fog/stratus product images

Hurricane Earl

August 29th, 2010
GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images

GOES-13 10.7 µm IR images (above) and 0.63 µm visible images (below) from the CIMSS Tropical Cyclones site showed Hurricane Earl after the storm reached Category 1 intensity on 29 August 2010. A Central Dense Overcast (CDO) could be seen developing in the images as Earl approached the Leeward Islands.

GOES-13 0.63 µm visible images + surface reports

GOES-13 0.63 µm visible images + surface reports

A comparison of 85 GHz microwave images at 11:02 UTC and 17:23 UTC (below) revealed the increasing organization of banded convective elements around the center of the hurricane.

SSMI/S-16 and AMSR-E 85 GHz microwave images

SSMI/S-16 and AMSR-E 85 GHz microwave images

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GOES-15 0.63 µm visible images

GOES-15 0.63 µm visible images

As a part of the GOES-15 Post Launch Science Test, the satellite was placed into Rapid Scan Operations (RSO) mode, providing images periodically at 5-minute intervals. GOES-15 0.63 µm visible images (above; also available as a QuickTime movie) and 10.7 µm IR images (below; also available as a QuickTime movie) showed two distinct convective bursts that were developing within the CDO region (the 15 UTC and 18 UTC positions of the center of Earl are marked on the images). The coldest cloud top IR brightness temperatures were -86º C (darker violet color enhancement) at 16:15 UTC and again at 19:25 UTC.

The far eastern portion of the island of Guadeloupe can be seen mapped in dark blue along the lower left edge of the GOES-15 images.

GOES-15 10.7 µm IR images

GOES-15 10.7 µm IR images

Be sure to check out the PREDICT Field Experiment Blog for additional insights on other tropical cyclone activity in the Atlantic basin.