MIMIC Total Precipitable Water product (click image to play animation)

Abundant moisture associated with a strong tropical wave (18 UTC surface analysis) fueled strong thunderstorms which produced record-setting rainfall at San Juan, Puerto Rico on 18 July 2013. AWIPS images of the MIMIC Total Precipitable Water (TPW) product (above; click image to play animation) showed the westward motion of the tropical wave, which exhibited TPW values greater than 50 mm or 2.0 inches (darker orange color enhancement) over a broad area — in fact, TPW values in the vicinity of Puerto Rico reached 60 mm or 2.4 inches on 18 July. Much drier air with significantly lower TPW values (30-35 mm or 1.2-1.4 inches, cyan to darker blue color enhancement) followed in the wake of the tropical wave passage; this dry air was likely the leading edge of a westward pulse of the Saharan Air Layer or SAL (real-time SAL images).

McIDAS images of 4-km resolution GOES-13 10.7 µm IR channel data (below; click image to play animation) showed numerous clusters of thunderstorms with very cold cloud top IR temperatures — IR brightness temperature values were as cold as -82º C (violet color enhancement) at 17:10 UTC.The location of San Juan is marked by the ‘*‘ symbol on the images.The GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes.

GOES-13 10.7 µm IR channel images (click image to play animation)

A 1-km resolution POES AVHRR 12.0 µm IR image (below) showed a strong thunderstorm beginning to move over the far eastern end of Puerto Rico at 19:35 UTC.

POES AVHRR 12.0 µm IR image (with METAR surface reports)

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GOES-13 false-color Red/Green/Blue (RGB) image

Tungurahua is an active stratovolcano in Ecuador (Wikipedia); a Landsat-8 false-color image showed the partially snow-covered dome of the volcano on 13 July 2013. On the following day, the Washington Volcanic Ash Advisory Center issued a volcanic ash advisory due to an explosive eruption that occurred at 11:51 UTC on 14 July 2013. A GOES-13 false-color Red/Green/Blue (RGB) image created using the NOAA/CIMSS GOES-R Volcanic Ash Detection Algorithm (above) highlighted a warm thermal anomaly and a volcanic cumulonimbus (based upon very rapid cloud top cooling rates and cold IR brightnesss temperature values) minutes after the eruption began — during the “11:45 UTC” GOES-13 image, the satellite was actually scanning the region of the volcanic eruption at 11:58 UTC.

GOES-15 (left), GOES-12 (center), and GOES-13 (right) visible images

A comparison of the early stages of the volcanic cloud as viewed from GOES-15 (GOES-West), GOES-12 (GOES-South America), and GOES-13 (GOES-East) is shown with visible channel images (above) and IR channel images (below). The actual times that each of the satellites were scaning the region of the volcanic eruption are noted in the labels, and the images are shown in the native projection for each individual satellite.

The GOES-13 satellite was the first to detect to volcanic cloud, since it was scanning the area at 11:58 UTC (about 7 minutes after the beginning of the eruption). The oblique viewing angle from the GOES-15 satellite helped to highlight the darker gray appearance of the ash-laden volcanic cloud, and reveal the long shadow being cast to the west of the tall feature (estimated to be as high as 45,000 feet above ground level). The volcanic cloud appeared largest on the GOES-12 images due to the more direct viewing angle, as well as the later scan time.

GOES-15 (left), GOES-12 (center), and GOES-13 (right) IR images

Animations depicting the volcanic cloud evolution are shown using GOES-12 0.65 µm visible channel, 6.5 µm water vapor channel, and 10.7 µm “IR window” channel images (below). Since a large amount of water vapor is usually exhaled during such explosive eruptions, the extent of the volcanic cloud can be more easily followed on the water vapor channel images.

GOES-12 0.65 µm visible channel images (click image to play animation)

GOES-12 6.5 µm water vapor channel images (click image to play animation)

GOES-12 10.7 µm IR channel images (click image to play animation)

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Landsat-8 and GOES-13 views of Convection over Southern Wisconsin

The SSEC Data Center has started ingesting Landsat-8 data, and serving the data up as McIDAS AREA files via ADDE. The image above compares Landsat-8 visible imagery (in the blue part of the visible — near 0.50 µm) that has been scaled down by a factor of 6 from the native 30-m resolution with GOES-13 visible imagery that has been magnified by a factor of 5 from the nominal 1-km resolution. A full-resolution image from Landsat-8 of the convective cell just southeast of Ft. Atkinson, WI is shown here.

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Stereoscopic View of Tropical Storm Chantal

Tropical Storm Chantal, the third named storm of the northern Atlantic Tropical Season, has rapidly moved through the Lesser Antilles and into the eastern Caribbean Sea. The stereoscopic view of Chantal, above, uses visible (0.65 µm) imagery from GOES-12 (over the Equator at 60 W) and visible (0.63 µm) imagery from GOES-13 (over the Equator at 75 W) and shows Chantal as it moved between Martinique and St. Lucia. A similar image, but at 10.7 µm, is here. Coldest brightness temperatures northeast of the storm center were -78 C.

GOES-13 0.63 µm visible channel images (click image to play animation)

The GOES-13 satellite had been placed into Rapid Scan Operations (RSO) mode, providing images as frequently as every 5-10 minutes. Visible imagery (above; click image to play animation) revealed the presence of low-level convective outflow boundary cloud arcs along the western periphery of Tropical Storm Chantal. The appearance of these cloud arcs can be an indication that a tropical cyclone has encountered an area of dry air aloft (generally either from the Saharan Air Layer, or a mid-latitude dry air intrusion), which can sometimes have a negative effect on the rate of intensification of the storm. However, in this case, Chantal slowly intensified during the day as it moved over the warm waters and high ocean heat content that were in place over the western Caribbean Sea.

Morphed Microwave Estimates of Total Precipitable Water

The morphed animation of Total Precipitable Water (TPW) from the CIMSS MIMIC site, above, shows the maximum in TPW associated with Chantal moving west-northwestward across the tropical Atlantic on a path towards the Greater Antilles — likely Hispaniola. (Note to NWS WFOs: MIMIC TPW is available via LDM subscription and can be displayed in AWIPS). Several products available at the CIMSS Tropical Cyclones website (in addition to the MIMIC TPW above) can be used to diagnose the environment around the system and the strength of the system.

Objectively-determined Overshooting Tops over the Tropical Atlantic, 1915 UTC 9 July 2013

For example, Tropical Overshooting Tops (TOTs) (at this site), are related to the vigor of the convection that is sustaining the Tropical Storm. The objectively-determined TOTs, above, show a cluster within the convective envelope of the system. This suggests ongoing strong convection and a storm that is at minimum maintaining its strength at present. (Given that the upper-level environment can change rapidly, the presence of TOTs may not be well-correlated with strengthening, however). This line plot shows the maximum sustained winds of the system plotted with the number of TOTs near the system.

Saharan-Air Layer Analysis, Tropical Atlantic, 1800 UTC 9 July 2013

Dust from the Sahara Desert that is lofted by winds and transported into the atmosphere above the tropical Atlantic has a well-known suppressing effect on convection and therefore tropical cyclone development and strengthening. It is often visible from satellite. The SAL analysis, above, (from this site) shows little to impede Chantal as it moves into the Caribbean. Most of the SAL at present is behind the storm.

Wind Shear and Tendency, derived from Satellite data, 1800 UTC 9 July 2013

Other data at the CIMSS Tropical Cyclones site can be used to judge the environment that the storm is in. Around Chantal, for example, wind shear values (above, from here) are modest (and decreasing), but they increase in the direction that the storm is moving. Oceanic Heat Content in the Caribbean Sea surrounding Chantal is sufficient to support strengthening, and the current National Hurricane Center forecast does modestly strengthen the storm before landfall on or near Hispaniola.

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