CHAPTER 11 TROPICAL  FORECASTING Forecasting in the Tropics is a difficult problem. It necessitates  a  good  meteorological  and  physics background, vast amounts of climatological knowledge, a keen mind’s 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 manual. 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, NAVEDTRA  10370. 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 climatology. TROPICAL CYCLONE FORECASTING 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. THE PROBLEM Forecasting  tropical  cyclones  evolves  into  the following  problems: 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 11-1