barge not to sail over these sea lanes. Meanwhile, if
the total index value reaches up to 10 – 12, the risk
level is said to be very high, which means it is really
dangerous for a barge to sail over the region. But
figure 4 shows that the conditions where the risk level
is categorized very high rarely happen over closed sea
waters regions over Indonesia in normal years.
Therefore, it assumes that this condition can occur
when a cyclone or other atmospheric–ocean
disturbance phenomenon happened.
Based on the risk index variation map in January
(Figure 4a), the risk level is very high over the South
China Sea and some parts of Pacific and Indian Ocean
near Sumatra and the south part of Java Island. The
high-risk level region occurred around Java Sea, a
small fraction of Banda, Arafura, and Timor Sea.
While moderate-risk level region mostly occurred
over Karimata Strait. The lowest risk level region was
located around Makassar Strait, Molucca Sea, and the
northern part of Banda Sea. This low-risk level region
is commonly located over small sections of closed sea
waters between some islands surround it as a great
barrier and obstacle when the wind blows over it.
In February, the risk shipping level over the
Indonesian sea was mostly moderate, such as over
Karimata Strait, Java Sea, Banda Sea, Arafura Sea,
and Celebes Sea. The other region among closed
seawater regions over Indonesia possesses a lower
risk level, such as along some parts of Makassar Strait
and some part of Molucca Sea. While, since it is in
the Asian monsoon period, the risk level over South
China Sea and along the Pacific Ocean is categorized
as very dangerous. The atmospheric–ocean parameter
risk level variability tends to get lower in March, low-
risk level region expands over several regions,
including Karimata Strait, a small fraction of Java
Sea, Makassar Strait, and Molucca Sea. While the rest
areas possess a moderate risk level of sailing. In
April, the lower risk level region tends to get wider
and covers almost all part of closed sea waters in
Indonesia. The high-level risk region starts to occur
over Indian Ocean, it moves from Pacific Sea in DJF
period to Indian Ocean as it is approaching JJA
period. In the last month of the first transition phase
period of MAM, the atmospheric–ocean parameter
risk index over the southern part of Indonesian sea
start to increase significantly, especially over Indian
Ocean near Australia.
In Australian monsoon period in June, the
atmospheric–ocean parameter risk level elevated,
especially over Arafura, Banda, and Timor Sea along
with the strengthening of the Australian Monsoon.
This high-risk level region then expands and reaches
its maximum in July 2013 and starts to slightly
decrease in August. In the second transition period in
September, the atmospheric–ocean parameter risk
level generally moderate over all parts of Indonesian
sea, except in a small fraction of Celebes Sea,
Makassar Strait, and Molucca Sea. In October, the
lower risk level region starts to get wider and covers
almost all parts of the Indonesian sea. While, both
Pacific and Indian Oceans possess moderate to high-
risk levels. In the last month of SON period,
November, the low-risk level region became wider
and covered all parts of the closed seawater in
Indonesia. This condition changed significantly in
December when the Asian monsoon began to be
strengthened. The high-risk level region observes
over the dominant part of South China Sea and along
the Pacific Ocean. Karimata Strait and Java Sea
possess moderate risk level of sailing safety, while the
other generally tend to have the low-risk level of
sailing safety.
4 SUMMARY AND CONCLUSION
The wind speed over Indonesia has a distinctive
pattern where the strongest wind region is commonly
located near the ocean, both in Pacific and Indian
ocean, while it starts to decrease as it approaches the
Indonesia sea region, closed waters between the
islands. The significant wave height pattern generally
follows the surface wind pattern as it is the wave
generator factor in the free ocean. Generally, the
characteristics of waves in Indonesian sea waters
have patterns associated with the monsoonal wind
cycle. In Asian monsoon period (DJF), wind speed
generally, starts to increase in December and gets
stronger in January but then tends to weaken in
February. January possesses the strongest wind
distributed around South China Sea and Pacific
Ocean with velocity ranges from 13 up to more than
17 knots.
Compared to wind profile and wave height
variation, rainfall intensity pattern possesses a higher
variability, both in land and marine region. In Asian
monsoon period, the rainfall intensity reaches its
maximum in December 2013 with heavy rainfall
areas distributed around the South China Sea and Java
Sea region with range values from 20–50 mm/day. It
starts to decrease in January, more often significant in
February. In transition periods, rainfall intensity tends
to have a higher value over land area rather than over
marine region. In Australian monsoon period, rainfall
intensity tends to be slightly higher over marine
regions than land areas. Its distribution was varied
and random, but it started to significantly decrease in