Tropical Storm Rafael

October 15th, 2012 |
Suomi NPP VIIRS 11.45 µm IR channel and 0.8 µm Day/Night Band image

Suomi NPP VIIRS 11.45 µm IR channel and 0.8 µm Day/Night Band image

Tropical Storm Rafael was slowly intensifying over the Atlantic Ocean north-northeast of Puerto Rico on 15 October 2012. McIDAS-V images of Suomi NPP VIIRS 11.45 µm IR channel and 0.8 µm Day/Night Band data at 05:33 UTC (above; courtesy of William Straka, CIMSS) showed cloud top IR brightness temperatures colder than -85 C (violet color enhancement), as well as city lights from the islands of the Dominican Republic, Puerto Rico, and other nearby islands.

A 08:25 UTC SSMI-15 85 GHz microwave image from the CIMSS Tropical Cyclones site (below) revealed a ragged banding structure that suggested Rafael was trying to form an organized eye.

SSMI-15 85 GHz microwave image

SSMI-15 85 GHz microwave image

A comparison of AWIPS images of POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel data at 14:08 UTC (below) offered a close-up view of the central dense overcast region of Rafael, with transverse banding forming along the periphery and convective overshooting tops with IR brightness temperatures as cold as -93 C (darker violet color enhancement).

POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images

POES AVHRR 0.86 µm visible channel and 12.0 µm IR channel images

 

Large storm over the Arctic Ocean

October 15th, 2012 |
Suomi NPP VIIRS 11.45 µm IR channel images (click image to play animation)

Suomi NPP VIIRS 11.45 µm IR channel images (click image to play animation)

 

AWIPS images of Suomi NPP VIIRS 11.45 µm IR channel data (above; click image to play animation) showed a very large storm moving slowly across the Arctic Ocean during the 13 October – 15 October 2012 period. Large areas of stationary sea ice could be seen over portions of the Arctic Ocean.

Widespread convective elements were apparent on the IR images, which were a result of an unstable air mass due to cold air advection across the region — this deep layer of instability could be seen on the 15 October 00 UTC rawinsonde data plot from Barrow, Alaska (below).

 

Barrow, Alaska rawinsonde data  (00 UTC 15 October)

Barrow, Alaska rawinsonde data (00 UTC 15 October)

The Area Forecast Discussion issued by the Fairbanks National Weather Service forecast office summarized the impacts of this large storm along the arctic coast of Alaska:

NORTHERN ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FAIRBANKS AK
501 AM AKDT MON OCT 15 2012

.DISCUSSION...
THE GFS AND NAM COMPUTER WEATHER FORECAST MODELS ARE IN GOOD
AGREEMENT THROUGH 4 AM WEDNESDAY. A LARGE AND LONG-LIVED LOW
PRESSURE SYSTEM NOW ABOUT 600 MILES NORTHWEST OF BARROW IS
GRADUALLY WEAKENING...AND DRIFTING SLOWLY TO THE NORTHWEST. THE
WEATHER AT SEA IN THE CHUKCHI AND ALONG THE ALASKAN CHUKCHI SEA
COAST IS THE MOST IMPORTANT ASPECT OF THIS MORNINGS FORECASTS.

COLD AIR HAS BEEN STREAMING DOWN FROM THE FAR NORTHWESTERN CHUKCHI
SEA THROUGH BERING STRAIT. THE EDGE OF THE ARCTIC ICE PACK IS NOW
ABOUT 400 MILES NORTHWEST OF BARROW...AND ADVANCING SOUTHWARD 10
TO 15 MILES A DAY.

THE ABNORMALLY LONG FETCH OVER THE CHUKCHI SEA DOWN TO THE ALASKA
ARCTIC COAST WEST OF CAPE HALKETT IS THE MAIN FACTOR IN THE
BUILDUP OF ROUGH SEAS. THE INCOMING SWELLS AT BARROW HAVE BEEN
FROM 4 TO 6 FEET HIGH. DUE TO ABNORMALLY FREQUENT WEST WINDS IN
THE ALASKAN ARCTIC THIS SUMMER AND FALL...THE WIDE BEACH AND
SHALLOW WATER OUT FROM SHORE HAVE BEEN MUCH REDUCED. AS A
RESULT...THE INCOMING SWELLS ON THE ALASKAN NORTHERN ARCTIC COAST
ARE NOT BREAKING SEVERAL HUNDRED YARDS OFFSHORE AS THEY USUALLY
DO. INSTEAD...THE INBOUND SWELLS ARE NOT BREAKING UNTIL REACHING
THE SHORELINE. THE RUN UP OF THE BREAKING SURF IS CONSIDERABLY
MORE NOW THAN IT WOULD BE UNDER NORMAL SHORELINE CONDITIONS.

POLAR ORBITING SATELLITE IMAGERY HAS SHOWN EXTENSIVE CONVECTIVE
CLOUDS OVER THE CHUKCHI SEA. THIS...AND THE EARLY MORNING WEATHER
BALLOON DATA FROM BARROW...KOTZEBUE...AND NOME...INDICATE AN
UNSTABLE AIR MASS. THIS FEATURE GIVES A LARGER TRANSFER OF
ENERGY FROM THE WIND TO THE SEA. THIS HAS BEEN THE CASE FOR
SEVERAL DAYS NOW.