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Weather
Monsoon is derived from the Arabic word for wind.
Cruising sailors know it is a seasonal wind: for part of the year
it blows one way, then turns around and blows the other way. The weather
in the Andaman Sea, like much of southern Asia, is divided into two
main seasons — the typically dry, moderate northeast monsoon
and the wet and sometimes wild southwest monsoon — with two shorter
transitional seasons between the two monsoons.
The northeast monsoon, from December
to March, is the dry season, characterised by gentle to gusty shore
breezes and clear skies. It is the best time to explore the west
coast islands of southern Thailand and northern Malaysia. Rain is
rare. It is the coolest time of year. The winds come from the northeast,
off southern Thailand and the Malay Peninsula, so there is virtually
no swell. Calms are common, lasting from hours to several days and
motorsailing is often necessary, particularly in sheltered cruising
grounds such as Phang Nga Bay, between Phuket and the mainland.
It is also the high season for the region's robust tourism industry,
which reaches its peak during December and January.
This is also the time when the many transient yachts that congregate
in Phuket-Langkawi set off across the Indian Ocean — heading
for the Andaman Islands, Sri Lanka or Chagos en route to the Red
Sea or South Africa. Most delay their departure until early January,
after the end of the tropical-storm season affecting South Asia
and the mid-Indian Ocean. This window of opportunity diminishes
toward the end of February when the northwest monsoon begins to
lose steam — it's not that unusual for sailors who depart late
to find they have to motor most or all the way to Sri Lanka.
Phuket-Langkawi is outside a tropical storm zone, though a rare
cyclone will drift out of the Bay of Bengal to lash the area once
every 20 years or so.
The southwest monsoon lasts from
June to September. In southern Asia, when people refer to the
monsoon season, as a synonym for the rainy season, it's
the southwest monsoon they are talking about. It's hot, humid and
wet.
The southwest monsoon tends to blow harder and more consistently
than the northeast monsoon, with winds of 10-30 knots. Two-metre
seas are typical, with many rain squalls. Periods of unsettled weather
tend to last a week or so, followed by a period of relative calm
before the weather turns sour again.
Squalls last from 20 minutes to a couple hours, with heavy rains
which can reduce visibility to a matter of metres, and strong winds
which can suddenly shift, changing direction in relation to the
centre of the squall. Usually, an approaching squall can be seen
from a long way off, typified by a towering dark cloud, allowing
a sailor to either seek shelter if close to land or steer clear
of dangers in anticipation of reduced visibility.
Diving and snorkelling are generally less appealing at this time
of year, since underwater visibility is reduced by stirred silt.
There are many secure anchorages during either monsoon, but fewer
during the southwest monsoon, when generally shelter is found behind
offshore islands, unlike the northwest monsoon when the whole length
of the coast provides potential shelter.
But if you don't mind the odd blow, and rain, the southwest monsoon
provides wonderful cruising opportunities, including the chance
to explore anchorages unavailable at other times of year. It's also
the tourist low season, and you will find many smaller islands with
bungalow operations that cater to tourists or backpackers are virtually
deserted. You will have the beach and restaurant to yourself. And
the pace slows to a crawl, the ideal situation for meeting and interacting
with local people.
There is a danger at this time of year, though: sumatras.
These fierce winds come from the west, the direction of the Indonesian
island of Sumatra, their namesake. Sumatras are much more common
in the southern Malacca Strait, rarer as you move farther north.
On average, Langkawi will be hit by about two sumatras a year, Phuket
perhaps one.
Sumatras first appear as a low, dark cloud along the western horizon.
They come quickly, often allowing barely enough time to reduce sail.
They are most common at night or early morning, when they hit without
warning, bringing rain and winds up to 60 knots. Like squalls, they
can last for 20 minutes to several hours. Lightning strikes are
a constant danger. If you plan to leave your yacht in Langkawi for
an extended period on a mooring with some exposure to a west wind,
it would be prudent to take down your awnings — a breakwater
or low-lying land will not protect them.
The transitional seasons can last
a month or two or longer, each year is different. The winds tend
to be listless and fluky, coming from any direction, with occasional
squalls and frequent periods of calm. There is meteorological data
regarding wind tendencies during the transitional periods, but this
is of little practical value to a mariner, except to say that winds
from the east to south are the least likely.
The April-May transition is the hottest time of year, with temperatures
of 27 to 36 degrees Celcius (80-95F), high humidity and occasional
squalls. It can be very wet or not wet at all. The October-November
transition is similar, but typically sees more rain, and is not
as hot.
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