GOES-13 (left) and GOES-12 (right) visible imagery images

Tropical Storm Dorian has formed in the far eastern Tropical Atlantic, just west of the Cape Verde Islands. The visible imagery above, from GOES-13 (left) and GOES-12 (right) shows the evolution of the storm in the morning on July 25th. The position change in six hours between 0845 UTC and 1445 UTC suggests a steady west-northwest movement. GOES-12 (scheduled to be decommissioned on 16 August) sits above 60 W vs. 75 W for GOES-13. Accordingly, GOES-12 has a more top-down view of the storm (near 35 W on July 25th) and GOES-13’s view is more oblique. This explains the more circular presentation in the GOES-12 imagery compared to GOES-13. A similar difference in geometry is apparent in the 10.7 µm imagery shown below. A slow increase in the storm organization is also obvious in the animation below.

GOES-13 (left) and GOES-12 (right) 10.7 µm imagery imagery

MIMIC Total Precipitable Water, 1300 UTC 25 July 2013

Future development of the storm depends strongly on the environment through which the storm will move. Morphed microwave data (above) suggests that the atmosphere ahead of the storm is dryer, as total precipitable water values are less than 40 mm in the central tropical Atlantic. However, there is robust feed of moisture from the Equator near the South American coast into the storm and ocean surface temperatures are progressively warmer along the projected path of the storm. Sounder data from this site, shown below, suggests that Dorian is moving into a dryer and more stable environment. (In the imagery below, Dorian is the small storm at the far eastern edge of the sounder footprint, near 15 N and 35 W)

GOES-12 Sounder DPI values of Lifted Index and Total Precipitable Water, 1300 UTC on 25 July 2013

ASCAT Scatterometer winds, and Total Precipitable Water, around 1100 UTC on 25 July 2013

Scatterometer winds from ASCAT, above, show tropical storm-force winds north of the storm center. The storm itself is embedded within a rich moisture feed from the ITCZ. Further information and graphics on the storm are available at the CIMSS Tropical Weather Website and the CIMSS GOES-R Tropical Overshooting Tops Website. Refer to the National Hurricane Center website for official forecasts and storm discussions. People along the southeast coast of the United States and in the Caribbean Sea should monitor the progress of this early-season storm.

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Suomi/NPP VIIRS 3.74 µm shortwave IR and 0.7 µm Day/Night Band images

MODIS 3.7 µm shortwave IR image

POES AVHRR 3.74 µm shortwave IR image

The shallow-water natural gas drilling rig Hercules 265 (located in about 150 feet of water, 55 miles off the coast of Louisiana) caught fire late in the evening on 23 July 2013. This fire event was captured by polar orbiting satellites with VIIRS, MODIS, and AVHRR instruments (above) and also by the GOES-13 satellite (below). VIIRS data from the Suomi/NPP satellite (top image) showed a warm thermal signature (yellow color enhancement) co-located with a region of enhanced brightness on the Day/Night Band image at the location of the burning rig. Shortwave IR brightness temperatures were not particularly warm on the VIIRS and MODIS images — 37.5º C and 31.5º C, respectively — because thin high clouds were overspreading the region, and those cold clouds were also being sensed by the radiometer. However, an apparent small break in the high clouds allowed the AVHRR instrument to detect a maximum shortwave IR brightness temperature value of 50.5º C (red color enhancement).

GOES-13 detected a jump in 3.9 µm pixel brightness temperature on the 03:45 UTC image (the actual scan time of that region was 03:50 UTC, or 10:50 PM CDT), as shown below. The brightness temperature increased from 23º C to 29º C as the fire was detected. The thin clouds evident in the imagery were likely responsible for the relatively cool IR brightness temperatures exhibited by this fire.

GOES-13 3.9 µm images at 03:32 and 03:45 UTC

GOES-13 3.9 um shortwave IR imagery spanning the first several hours of the fire (below; click image to play animation) captured the appearance of the initial fire hot spot, followed by the periodic partial obscuration from the satellite view as high clouds moved over the region. The fire was declared to have stopped burning early in the day on 25 July, after the well became clogged with sand and sediment, shutting off the supply of natural gas that had been fueling the fire.

GOES-13 3.9 µm shortwave IR images (click image to play animation)

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Suomi NPP VIIRS 0,7 µm Day/Night Band and 11.45 µm IR channel images

A comparison of AWIPS images of Suomi NPP VIIRS 0.7 µm Day/Night Band and 11.45 µm IR channel data (above) showed a large mesoscale convective system in southwestern Arizona at 08:40 UTC or 2:40 am local time on 20 July 2013. With ample illumination from the Moon (which was in the Waxing Gibbous phase, at 96% of full), the “visible image at night” capability of the VIIRS Day/Night Band image allowed shadowing from overshooting thunderstorm tops to be clearly seen; the coldest cloud-top IR brightness temperature of the overshooting tops was -83º C (violet color enhancement). In addition, numerous cloud-to-ground lightning strikes were associated with the MCS at that time. A few hours earlier, this storm had produced reports of wind damage in the Phoenix area just after 05 UTC (SPC Storm Reports).

With the arrival of daylight, McIDAS images of GOES-15 (GOES-West) 0.63 µm visible channel data (below; click image to play animation) revealed the emergence of a well-defined and relatively compact Mesoscale Convective Vortex (MCV) that continued to move westward across southern California during the day. The MCV also played a role in helping to iniitate additional convection in areas such as the San Bernadino Mountains of southern California.

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

A comparison of Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images at 20:05 UTC (below) showed that the clouds associated with the MCV were primarily low to mid-level clouds, which exhibited IR brightness temperatures that were generally warmer than -20º C.

Suomi NPP VIIRS 0.64 µm visible channel and 11.45 µm IR channel images

For aditional information on MCVs, see the VISIT lesson “Mesoscale Convective Vortices“. For additional information on VIIRS imagery, see the VISIT lesson “VIIRS Satellite Imagery in AWIPS“.

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MTSAT-2 visible (daytime) and IR (night-time) images

A sequence of MTSAT-2 0.675 µm visible channel images (during daytime) and 10.8 µm IR channel images (during the night) revealed the signature of what could be a “midget” tropical cyclone which was moving westward across the western Pacific Ocean during the 17 July – 19 July period (above; click image to play animation).

MTSAT-2 6.75 µm water vapor channel images with overlays of satellite wind derived deep-layer wind shear from the CIMSS Tropical Cyclones site (below; click image to play animation) showed that the region near 21º North latitude 130º East longitude was experiencing generally light to moderate northeasterly wind shear during this time period.

MTSAT-2 water vapor images + deep layer wind shear

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