As the 2006 Atlantic hurricane season nears its historical peak in mid September,
Hurricane Florence is making its way northward through the western Atlantic near
Bermuda. Although Florence is the sixth named storm of the season, unlike last year's
record breaking season, there has been a scarcity of hurricanes and as of yet no major
hurricanes. Ernesto briefly reached minimal hurricane intensity. Florence, which
formed into a tropical depression back on the 3rd of September 2006, became the second
hurricane of the season as it approached Bermuda but has and is not expected exceed
Category 1 intensity. The following series of images from the the Tropical Rainfall
Measuring Mission (or TRMM) satellite chronical Florence's progress across the Atlantic.
The first TRMM image on the right shows Florence as it was passing well to the northeast
of the Leeward Islands. The images were taken at 2017 UTC (4:17 pm EDT) 7 September
2006. With its suite of active and passive sensors, TRMM is designed to measure
rainfall from space but has also proven itself to be a valuable tool for examining
tropical cyclones. The first image shows instantaneous rain rates associated with
areas of convection within the storm. Rain rates in the center swath are from the TRMM
Precipitation Radar (PR), while those in the outer swath are from the TRMM Microwave
Imager (TMI). The rain rates are overlaid on infrared (IR) data from the TRMM Visible
Infrared Scanner (VIRS). TRMM reveals that Florence then consisted of an unusually
broad area of scattered light (blue) to moderate (green) rain with little evidence of
organization as indicated by the lack of an eye or banding features (curvature). Indeed
the center of circulation as indicated by the storm symbol was on the southern edge of
the convective activity.
The next image was obtained from the same TRMM overpass as the previous image and gives
a 3D perspective of the storm courtesy of the TRMM PR. The view is to the northeast.
TRMM revealed the presence of several deep convective towers (shown in red) with tops
exceeding 15 km. Such towers can be an indication of future intensification as they mark
areas of deep convection within the storm. However, as Florence had such a broad
circulation and was not-well organized with the center of circulation at the edge of the
cloud mass, intensification remained slow. At the time of these images, Florence had
sustained winds estimated to be 45 knots (52 mph) by the National Hurricane Center (NHC).
On the 8th of September, as Florence continued to trek off to the northwest, it maintained
intensity as a weak tropical storm. On the 9th, the system finally started to become more
organized and strengthened into a strong tropical storm. This next image from TRMM was
taken at 0233 UTC 10 September (10:33 pm EDT 9 September) as Florence was starting to
approach Bermuda. The IR data show that Florence has excellent outflow aloft as indicated
by the symmetry in the expanded cloud pattern (white areas). However, Florence was also
feeling the effects of midlevel wind shear as evidenced by the somewhat elongated features
in the rain field (note the northwest-southeast stretching of the rain bands surrounding
the center). NHC was now estimating the maximum sustained winds to be 55 knots (63 mph).
The next day, on the 10th, Florence finally reached hurricane intensity as it turned to
the north ahead of a midlatitude trough and headed in the direction of Bermuda. These
final two images were taken at 2045 UTC (4:45 pm EDT) September 10th and show Florence as
it was approaching Bermuda. The first one shows rain bands circling a rather large eye,
which contains an area of intense rain (dark red arc) in the northwest eyewall. The
southeastern part of the eyewall, however, appears ragged. Most of the rain is ahead of
the storm (the broad blue and green area indicating light to moderate rain, respectively).
The final 3D image provides a unique perspective of the rainbands spiraling in towards the
center of Florence's large eye. At the time of these images, Florence was a Category 1
hurricane with maximum sustained winds of 80 knots (92 mph). The storm continued to move
north, and on September 11th, the center of Hurricane Florence passed just 60 miles to the
west of Bermuda, which reported hurricane force wind gusts and downed power lines.
Florence is now expected to accelerate off to the northeast before becoming extratropical
south of Newfoundland.
