I'M - National Archives and Records Administration

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1W 4 MV
WEATHER AND CLIMATE
Rer: (a) USAF 1st Weather Wing Special Studies 105-11/ "
(month) Climate of Southeast Asia"
(b) USqF lst Weather Wing Special Studies 105-9/ "
(month) Climate of the Republic of Vietnam -
1. September. Vietnam continues under the influence of the
southwest monsoon during September; however 9 late in the month
the northern provinces may be affected by weather conditions
associated with the Intertropical Convergence Zone. The IOTZ
brings an increase in cloudiness with cumulus clouds normally
forming by mi Porning, lowering and increasing in amount to
become broken ,vercast by midafte-noon. At night these cloudsbreak
up. There are a great desa of middle and high clouds in
September. Temperature decreases along the eastern coastal
plain by ~4 to 6 degrees F. Variations resulting from forest
cover may be strong. Maximum temperature below vegetation
canopies is lower while the minimum temperature is higher than
those observed in open area. In open areas, on still nights,
cool air collects in sinkholes and narrow ravines and ground
fog forms earlier there than over surrounding ground.
2. October 0 Most of the Republic of Vietnam is in the autumn
transition season between the southwest and northeast monsoon.
During the last half of October the northern portion of the
country comes completely under the influence of the northeast
monsoon. As the Intertropical Convergence Zone passes through
the Republic of Vietnam there are several days of scattered
heavy precipitation, but monthly totals remain low at most locations.
In the northern portions of the east coastp rainfall
amounts increase. The majority of precipitation falls from
afternoon and evening showers or thunderstorms but when signs
of the northeast monsoon appear, drizzle falls from stratus
along the east coast. Showers are generally intense.but are
of short duration. There is considerable variation in October
rainfall from one year to another and from one location to
another. October is a wet season month, The biggest rainfall
increases are observed around Hue. October and November are
the wettest months of the year along the east coast. Maximum
typhoon activity in the South China Sea occurs during October.
The storms tend to move farther inland before dissipating.
During the period from 1947 to 1965, ten storms, of which six
maintained typhoon winds (65 knots or more)p moved inland over
the Republic of Vietnam. Torrential rains may occur over wide
areas, particularly in the mountains, resulting in flooding
along river channels and in delta and coastal regions. The
poorest tractionability occurs this month along the northern
coast. Abnoimal tides associated with high seas and swells
contribute to flooding in coastal regions,
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