Remnants of Hurricane Paloma

November 14th, 2008 |
GOES-12 visible and 3.9 µm shortwave IR images

GOES-12 visible and 3.9 µm shortwave IR images

GOES-12 visible (daytime) and 3.9 µm shortwave IR (night-time) images (above) showed a distinct swirl of clouds drifting northward across the Gulf of Mexico on 13 November14 November 2008. This cloud swirl was actually the remnants of Hurricane Paloma, which had intensified to a Category 4 hurricane and made landfall over Cuba on 08 November. Note that there were a few weak convective bursts forming near the center of the swirl, but these were fairly short-lived.

AWIPS images of the 1-km resolution MODIS visible, 11.0 µm IR window, and 3.7 µm shortwave IR images (below) indicated that the swirl was comprised of primarily low-level clouds at 18:54 UTC, with IR brightness temperatures considerably warmer  than -20º C — in fact, the MODIS Cloud Top Temperature product displayed values that were generally in the 0º C to +10º C range.

MODIS visible + 11.0 µm IR + 3.7 µm IR images

MODIS visible + 11.0 µm IR + 3.7 µm IR images

The MIMIC Total Precipitable Water product (below) showed that the remnants of Paloma (which initially had drifted back southwestward over Cuba on 12 November) were embedded within a plume of higher precipitable water (30-45 mm, or 1.2-1.8 inches) as it moved northward across the eastern Gulf of Mexico.

MIMIC Total Precipitable Water

MIMIC Total Precipitable Water

As the remnants of Paloma reached the coast of the Florida panhandle on the morning of 14 November, explosive convective development was seen. This convection actually displayed a well-defined “enhanced-v” storm top signature on the GOES-12 10.7 µm IR imagery (below). Some back-building of the convection was also evident on the IR imagery — this convection produced a swath of heavy rainfall and flash flooding across parts of the Florida panhandle region, with a report of 9.25 inches of rain at Bloxham (located to the southwest of Tallahassee), and 2.61 inches falling at Tallahassee (setting a new rainfall record for the date). Radar-estimated storm total precipitation exceeded 14 inches.

GOES-12 10.7 µm IR images

GOES-12 10.7 µm IR images

A comparison of 1-km resolution NOAA-18 and 4-km resolution GOES-12 IR images (below) demonstrated the superior enhanced-v detection capability of higher spatial resolution data. The enhanced-v “delta-t” value (the difference between the coldest overshooting top and the warmest portion of the downstream warm wake) was an impressive 22.8º C, which would be a large delta-t value for a tornado or hail-producing supercell over the Great Plains region! This convection was also producing a good deal of cloud to ground lightning, as was noted on the early morning NWS Tallahassee Area Forecast Discussion:

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TALLAHASSEE FL
410 AM EST FRI NOV 14 2008

…SCATTERED SHOWERS AND THUNDERSTORMS HAVE BEEN DEVELOPING OVER OUR AREA…WITH A FEW OF THESE STORMS ALREADY EXHIBITING MARGINAL ROTATING UPDRAFTS AND IMPRESSIVE CLOUD TO GROUND LIGHTNING. THE LATEST RUC INDICATES MUCAPE FROM 350 J/KG OVER CENTRAL GA TO 1500 J/KG ALONG THE FL GULF COAST. THIS IS RATHER IMPRESSIVE FOR THIS TIME OF YEAR…

GOES-12 10.7 µm + NOAA-18 10.8 µm IR images

GOES-12 10.7 µm + NOAA-18 10.8 µm IR images

A blog post by Stu Ostro at the Weather Channel raises the interesting question of whether the energy associated with the remnants of Paloma played a role in the additional development of deadly tornadoes across North and South Carolina about 24 hours later?

Pacific moisture plume and strong jet

October 3rd, 2008 |
AWIPS images of water vapor composite

AWIPS images of geostationary satellite water vapor channel data

AWIPS images of geostationary satellite water vapor channel data (above) showed a long moisture plume moving across the Pacific Ocean toward the west coast of the US on 02-03 October 2008. A comparison of GOES-11 water vapor channel data with POES (AMSU) and SSM/I Total Precipitable Water (TPW) products (below) revealed that TPW values were as high as 50-60 mm (2.0-2.4 inches) within this moisture plume. The MIMIC TPW product suggested that this moisture plume originated over the western Pacific Ocean, southeast of Japan.

AWIPS images of POES TPW products and GOES water vapor channel

AWIPS images of POES TPW products and GOES water vapor channel

This moisture plume was associated with a strong polar jet stream, as seen by an overlay of hourly MADIS atmospheric motion vectors on GOES water vapor channel imagery (below).

GOES water vapor images + MADIS winds

GOES water vapor images + MADIS winds

The 18 UTC GFS model fields were forecasting maximum winds in the core of the jet to reach 170 knots (below) — there were a few MADIS wind vectors with speeds of 177-181 knots around that time (and a MADIS wind vector with a speed of 191 knots was seen at 21 UTC).

GFS winds + MADIS winds

GFS winds + MADIS winds

“Outflow boundaries” from Tropical Storms Hanna and Josephine

September 3rd, 2008 |
GOES-13 visible images (Tropical Storm Hanna)

GOES-13 visible images (Tropical Storm Hanna)

A series of low-level “outflow boundaries” was seen on GOES-13 visible imagery (above), propagating westward from the shield of high clouds associated with Tropical Storm Hanna, moving across the Bahamas on 03 September 2008. The air behind each of these pulses appeared to be quite dry, judging from the general lack of cloudiness in their wake.

AWIPS images of the GOES sounder 7.4 and 7.0 µm water vapor channels, the GOES sounder Total Precipitable Water product, and the GOES imager water vapor channel at 16 UTC  (below) indicated that a tongue of dry air existed over the Bahamas, sandwiched in between Hanna and the clouds/moisture over Florida. The rawinsonde report from Nassau in the Bahamas showed that the air mass was indeed quite dry within the 700-500 hPa layer.

AWIPS images of GOES sounder WV and PW, with GOES imager WV

AWIPS images of GOES sounder WV and TPW, with GOES imager WV channel

The MIMIC Total Precipitable Water (TPW) product (below) suggested that a large pocket of dry air (TPW values around 35 mm, cyan colors) was situated east of Hanna on 01 September, with part of this dry air then moving westward around the northern periphery of the tropical storm on 02-03 September.

MIMIC Total Precipitable Water (TPW) product

MIMIC Total Precipitable Water (TPW) product

The Saharan Air Layer (SAL) product (below) displayed a weak SAL signal (yellow to red colors) over the Bahamas region, supporting the idea that the pocket of dry SAL air had indeed moved around to the northwestern quadrant of Hanna. In addition, MODIS Aerosol Optical Depth values were slightly elevated over that region, suggesting the presence of African dust. Some of this dry mid-tropospheric SAL air may have been mixed downward behind the westward-propagating outflow boundaries noted on the GOES-13 visible imagery above.

Saharan Air Layer (SAL) product

Saharan Air Layer (SAL) product

Farther to the east, an even more pronounced “outflow boundary” was seen moving westward away from Tropical Storm Josephine, as shown on GOES-12 visible imagery (below). A strong SAL signature was depicted on the MIMIC TPW and SAL products, covering a large portion of the eastern Atlantic to the north of Josephine.

GOES-12 visible images (Tropical Storm Josephine)

GOES-12 visible images (Tropical Storm Josephine)

Bertha becomes a hurricane

July 7th, 2008 |

GOES-12 IR images (Animated GIF)

Hurricane Bertha became the first hurricane of the season in the Atlantic Basin on 07 July 2008,  setting a new record for the furthest-east named storm formation in the tropics. GOES-12 IR images from the CIMSS Tropical Cyclones site (above) showed increasing coverage of cold cloud top temperatures and the formation of an eye; microwave imagery from the polar-orbiting SSM/I instrument (below) began to show better evidence of an eye structure a few hours before the geostationary satellite imagery.

SSM/I microwave image

GOES-12 visible imagery (below) showed a closer view of the forming eye of the hurricane.

GOES-12 visible image

A plot of the CIMSS Advanced Dvorak Technique intensity estimate (below) showed that Bertha began a period of more rapid intensification during the early morning hours of 07 July.

Advanced Dvorak Technique intensity plot

Bertha had been moving northwestward over increasingly warmer Sea Surface Temperatures (below), which may have played a role in the intensification of the tropical cyclone.

Sea Surface Temperature data

UPDATE: Hurricane Bertha rapidly intensified into a Category 3 storm during the afternoon hours on 07 July, with the CIMSS ADT intensity estimation technique suggesting peak wind speeds near 115 knots. During this period of rapid intensification, Bertha also displayed a nice eye on satellite imagery (QuickTime animations: GOES-12 visible | GOES-12 IR). It is interesting to note that the MIMIC Total Precipitable Water product (below) indicated that dry Saharan Air Layer (SAL) air had wrapped completely around Bertha during the 05-08 July period — the presence of such dry air in close proximity to a tropical cyclone would normally be thought of as a negative factor for rapid intensification!

MIMIC Total Precipitable Water (Animated GIF)