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Table 1-1. Airflow, cloud and precipitation characteristics of the clima- tic periods illustrated in fig. 1-1. Fig. I-1A: NORTHEAST MONSOON (November-FebLirary) o The "dry season. II o An intense high pressure system over" central Asia produces cold air outflow and a stable airmass. o Strong northeast wi nds preva 11 in the lower atmosphere. .0 Although rainfall maxima are obSerVE!d along the northeast coast of Viet Nam and the southern peninsula of Thailand, the interior portions of Thailand are relatively cloud-free with little precipitation. o Occasional low pressure centers (tropical depressions or tropical storms) migrate westward from the Palcific or South China Sea to affect the southern portions of Thailand. These storms are usually rather weak, but are the main precipitation and convective cloud producers over inland areas of southeast Asia. Fig. 1-1B: SUMMER INTERMONSOONAL PERIOD (March-April) o Clear conditions, highest temperatures of the year. o Light variable winds that seldom have a recognizable general cir- culation pattern. Southerly winds from the Gulf of Thailand often bring moisture to inland areas. o Intense heati ng produces i sol ated airmass sho~{ers and thunderstorms. o Infrequently an intense mid-latitude trough transversing China will produce a northeast surge of sufficient intensity to penetrate through interior southeast Asia. Due to the availability of low-level moisture, these late season surges nlay be accompanied by destructive squall-line thunderstorms. Fig. 1-1C: ONSET SOUTHWEST MONSOON (May-.early June.l o Strong low-level winds from the southwest, weak winds aloft. o ITCZ moves rapidly north across Thailand with organized convection and extensive cloudiness. T ~, o The increased surface heating, low-level moisture, and weak vertical shear combine to produce the maximum frequency of thunderstorm days. .. " 5