Download AIR ClimateCast_Atlantic_Advisory

AIR ClimateCast® Atlantic Real-Time Advisory
AIR’s ClimateCast® Atlantic Real-Time Advisory provides a compact but powerful summary of the current environmental
conditions that affect tropical cyclone activity in the North Atlantic. Updated four times daily, the tool provides an overview of the
current season, including summary statistics and comparisons to long-term averages, as well as current conditions of three of
the most important ingredients in tropical storm development and landfall potential: sea-surface temperatures, wind shear and
steering currents.
Seasonal Overview (top left)
The top left panel shows an overview of the year's tropical cyclone activity in the North Atlantic to date, including any currently
active storms. Also provided are some general statistics for the “expected” number of tropical cyclones by the end of an
“average” season, as well as the expected number of tropical cyclones by the current date in an average season. Abbreviations
used are as follows:
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TS – Tropical storms
HU – Hurricanes
HU Minor – Hurricanes of Category 1-2 on the Saffir-Simpson Hurricane Wind Scale
HU Major – Hurricanes of Category 3-5 on the Saffir-Simpson Hurricane Wind Scale
Also shown is the accumulated cyclone energy (ACE) index, another frequently-used measure of seasonal activity. While ACE
can be calculated for individual storms, the ACE index provided in AIR’s ClimateCast for the Atlantic represents the sum—
across all tropical cyclones during the season—of the energy used, taking into account both the intensity and duration of each
storm. Generally, an above-average season can be defined as ACE >103, and a below-normal season as ACE < 66. Like the
tropical cyclone counts, ACE is provided for the current season to date, as well as for the average season (i.e. climatology)—
both overall and up to the current date in an average season.
Sea-Surface Temperatures (top right)
The map in the top right panel shows current sea-surface temperatures (SST) anomalies. These shaded areas indicate where
SSTs are either warmer or cooler than the long term average (climatology). Anomalously warm conditions can support activity
over and above levels expected based on long-term averages. The colored contours show actual current SSTs. Areas of the
ocean south of the dark blue contour (26.5°C) repre sent a rough estimate of those regions that can support strong, deep
convection and thus tropical cyclone development. Note that current SSTs are also shown as shaded areas in the Steering
Currents map immediately below.
Wind Shear Conditions (bottom left)
The figure on the bottom left shows the current vertical wind shear between about 1km and 10km altitude. Elevated vertical wind
shear conditions (10 m/s or greater) can disrupt the overall structure of the hurricane. Strong wind shear can impede cyclone
formation or weaken an existing storm. Thus, in the figure, low shear (shaded in reds) indicates regions where tropical storms
could potentially exist or intensify, and high shear (shaded in blues) indicates regions where environmental conditions may
inhibit further development.
Steering Currents (bottom right)
The bottom right figure shows, in contours, the ‘stream function’ at 500mb overlaid on current SSTs. The stream function can be
interpreted as the steering flow of the atmosphere, thus indicating the direction in which a tropical cyclone is likely to be headed.
The steering flow is fastest where the contours are tightly packed together and slowest where they are far apart. Red contours
surround high pressure centers, such as around the Bermuda High, a common summertime feature.
© 2010 AIR Worldwide
On each of these environmental condition maps is also shown the latest observed and forecast tracks, including the cones of
uncertainty, of any currently-active tropical cyclones. Note that the cones of uncertainty indicate possible areas of at least
tropical storm-force winds over the next 3 and 5 days. Also note, the cone of uncertainty indicates the region over which active
storms may potentially track, but the environmental conditions in place currently (SSTs, shear, steering) are susceptible to
change over the coming 1 to 5 days. In other words, the conditions contained in the cone of uncertainty are current conditions,
not conditions forecast once the storm reaches a forecast location. The steering and wind shear conditions are most likely to
change in the coming 1 to 5 days, whereas the SSTs and SST anomalies are more persistent—and indeed may persist for
several days and even weeks to come.
The data used in the production of AIR’s ClimateCast® Atlantic Real-Time Advisory comes from the official government
agencies charged with producing and distributing real-time weather and emergency management services, including the
National Hurricane Center (NHC), the National Centers for Environmental Prediction (NCEP), and the Climate Diagnostics
Center (CDC)—all part of the National Oceanic and Atmospheric Administration (NOAA).
© 2010 AIR Worldwide