GOES-13 0.63 µm visible images

McIDAS images of GOES-13 0.63 µm visible channel data (above, also available as a QuickTime movie) showed some interesting details associated with Tropical Storm Fiona in the central Atlantic Ocean on 02 September 2010: a series of intense convective bursts just south of a partially-exposed low-level circulation center, and a large northward-moving “outflow boundary” arc cloud. The GOES-13 satellite had been placed into Rapid Scan Operations (RSO) model, allowing images as frequently as every 5-10 minutes.

AWIPS images of the MIMIC Total Precipitable Water (TPW) product (below) revealed that a significant plume of TPW was being drawn northward from Tropical Storm Fiona into the circulation of Hurricane Earl. Note to National Weather Service forecast offices: see this site for details on how the CIMSS MIMIC TPW product can be added to your local AWIPS workstations, via Unidata LDM subscription.

MIMIC Total Precipitable Water product

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Morphed Microwave Imagery

Morphed Microwave Imagery (MIMIC), above, shows the evolution of the structure of Earl’s eye over the past 48 hours as Earl has strengthened from a Category 3 storm back to Category 4.

POES AVHRR 0.63 µm visible and 10.8 µm IR images

An AWIPS view of NOAA-16 AVHRR imagery (0.63 and 10.8 micron data, including ocean buoy reports) from just past 1200 UTC on 2 September, above, shows a well-defined eye nearly surrounded by convective clusters with temperatures near -75 C.

The northwestward motion of Hurricane Earl could be seen in a sequence of AWIPS images of POES AVHRR 10.8 µm IR and MODIS 11.0 µm IR data (below).

POES AVHRR 10.8 µm IR and MODIS 11.0 µm IR images

The visible imagery loop from this morning (below; also available as a QuickTime movie) from GOES-15 shows a steady motion just west of north.

GOES-15 0.63 µm visible channel images

Click here for a true-color image of Earl derived from Terra MODIS data.

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The parade of tropical impulses moving westward off of Africa into the tropical Atlantic that has produced Hurricanes Danielle and Earl, and Tropical Storm Fiona, has now yielded a new Tropical Depression, Number 9, that will become Gaston if it achieves Tropical Storm status. Some environmental conditions favor intensification, and some work against it.

The tropical depression is moving over warm sea surface temperatures, and is in an environment of low shear, two factors that argue for slow intensification of the system. However, an analysis of Saharan Air using Meteosat data (diagnosed as a split-window technique using 10.8 micron and 12.0 micron data) shows very dry air surrounding the storm. (See image below). Saharan Air Layers greatly impede the development of tropical cyclones. MIMIC Total Precipitable Water (from this site) also shows very dry air surrounding half of the developing storm. Water vapor imagery from GOES-East and from GOES-12 both show very dry air surrounding the tropical depression.

Visible and Infrared imagery from the storm this morning (below) show the impact of forward scattering and back-scattering on the detection of thin clouds. The visible imagery at 0815 UTC (left), when the sun is low in the sky and forward scattering dominates, suggests far more cloudiness than at 1745 UTC (right) when the sun is high in the sky and backscattering dominates. Infrared imagery, however, shows little change in the amount of detected cloudiness. Thin cirrus detection by visible satellite is easiest for very low sun angles; as the sun rises higher in the sky, cirrus clouds become less distinct in visible imagery. Note that GOES-R will include a detector sensitive to radiation at 1.3 microns to highlight cirrus clouds regardless of the Sun’s position (for example, see this comparison of MODIS visible, 1.3 µm near-IR, and 11.0 µm IR images).

For up-to-date information on the tropical systems in the Atlantic, visit the CIMSS tropical website, or the National Hurricane Center website.

(Added: TD #9 became Tropical Storm Gaston as of 5 PM EST on 1 September)

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AWIPS images of 1-km resolution POES AVHRR visible channel 1 (0.63 µm) and channel 2 (0.86 µm) along with IR channel 4 (10.8 µm) data (below) showed Hurricane Earl moving northwestward, just to the northeast of the Bahamas, on 01 September 2010. Earl’s intensity decreased from a Category 4 to a Category 3 storm during the day.

POES AVHRR 0.63 µm visible images

POES AVHRR 0.86 µm visible images

POES AVHRR 10.8 µm IR images

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