Forecasting in the Tropics is a difficult problem. It
necessitates a good meteorological and physics
background, vast amounts of climatological knowledge,
a keen minds eye that can observe the most minute
deviation in a mass of nearly homogeneous data, and
last, but not least, diligence and dedication in the
approach to the forecast.
The types of forecasts in the Tropics are the same
as anywhere, in that you encounter flight, route,
terminal, operational, general, fleet, local area, and
destructive weather forecasts, as well as pertinent
warnings and advisories.
Your concern in this chapter is with preparing local
area forecasts, including destructive weather warnings
and forecasts, and forecasting the movement of the Inter
Tropical Convergence Zone (ITCZ) and tropical waves.
The treatment of destructive weather warnings and
forecasts is limited to tropical storms and cyclones since
tornadoes are largely non-existent in the Tropics. Note
also, that thunderstorms are covered in chapter 5 of this
The Composite Warfare Oceanographic Support
Modules (CWOSM), Part 1, TM 0492, contains further
reading on severe weather features. Information may
also be found in the AG2 TRAMAN, volume 1,
LOCAL AREA FORECASTS
LEARNING OBJECTIVES: Analyze upper air
features and refer to local area climatology for
preparation of surface analyses and forecasts.
The importance of local and general area
climatology can have a profound impact on operations
in the tropics. It is in the preparation of the local area
forecast that this knowledge will be most beneficial.
During the analysis of the various charts, most
forecasters form a mental image of the forecast charts
and develop certain fundamental ideas as to the weather
in the area of responsibility (AOR) for the next 24 or 48
hours. Climatology serves as a guide for analysis and
forecasting within the AOR. The next step in the
procedure is to expand and refine these ideas.
The ideal approach to a local area forecast is to prog
the upper air features first as it is from the upper air
charts that the surface chart is eventually prepared. The
prognostic surface chart is then used as a basis for the
local area forecast. Of course other data must also be
considered in preparing the forecast, such as streamline
analysis, weather distribution charts, time sections, and
LEARNING OBJECTIVES: Recognize
synoptic features conducive to tropical cyclone
development. Identify situations affecting
movement and intensification of tropical
cyclones. Interpret tropical cyclone warnings.
There is at present no one formal procedure for
forecasting the development and movement of tropical
cyclones. This can be understood when one considers
the enormous complexity of the problem, the sparsity of
data in the oceanic tropical regions compared to that
available in the highly populated continents, and the
lack of ship reports from areas of tropical cyclone
activity. There are also regional influences to consider.
Avery obvious consequence of regional influences can
be demonstrated when you compare the North Atlantic
area with the North Pacific area. The North Pacific has
almost twice the tropical water area and also better than
double the average number of tropical cyclones per year.
Forecasting tropical cyclones evolves into the
formation, detection, location,
intensification, movement, recurvature, and decay.
The factors that enter into forecast preparation are
mainly dynamic (relating to the energy or physical
forces in motion), but there are also important
thermodynamic influences. For instance, tropical
storms will not develop in air that is drier and slightly