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Sector 10. Micronesia, Palau, and Guam

ber, the wind systems shift S and the island has another period of doldrums.

10.2

Squalls occur almost daily, particularly with E winds during

June and July. They are of short duration, with velocities of 15 to 30 knots. November and December are also squally months. The Northeast Trades blow from December to March over

10.2

Pohnpei Island. Gales have been reported during the trades, but are estimated to occur less than 5 per cent of the time. During April, E to SE winds increase in frequency and become pre- dominant in September and October. During this season, the winds are light and variable with frequent calms. Sudden vio- lent W to SW winds sometimes occur with the better devel- oped storms. These sometimes attain gale force.

10.2

The doldrums belt moves N over Pohnpei Island in June and

July, when the Northeast Trades give way to the Southeast Trades. A maximum of squalls and rainfall occurs at this time over the open sea. The doldrums move S in November and De- cember, and cause a secondary increase in squalls and pre- cipitation.

10.2

Showers and squalls are frequent, and occur at any time of

the year. Squalls are sometimes violent and have an average duration of 20 minutes. Thick cumulonimbus clouds immedi- ately precede these squalls, bringing gusty winds and heavy rain. Thunderstorms are rare. A 5-year average indicates only about 17 annually, fairly evenly distributed during the year.

Northeast and E winds prevail in the vicinity of Kapinga- marangi Atoll from December through April, with a frequency of 68 per cent and an average velocity of 11 knots. In May and June, variable winds prevail, with an average velocity of 7 knots. Calms occur about 11 per cent of the time. From July through September, SE winds occur 55 per cent of the time, with an average velocity of 8 knots. Calms occur about 5 per cent of the time. In October and November, winds average 7 knots from varying directions. Southeasterly winds pre- dominate and occur about 24 per cent of the time. Between October and January, W winds of 15 knots are experienced 10 per cent of the time.

10.2 10.2

Squalls and thunderstorms, with a diameter of 25 to 30

miles, are accompanied by winds averaging 15 to 25 knots, with occasional gusts up to 40 or 50 knots. Thunderstorms oc- cur on an average of 2 days per month from May through No- vember, and once a month for the rest of the year.

10.2

The Northeast Trades blow almost constantly from Decem-

ber to May over the Mortlock Islands and the Truk Islands. The average velocity is about 15 knots, with an occasional gust of 30 knots. Light variable winds can be expected from July to December. The influence of the doldrums is felt for a longer period (June to November) over the Mortlock Islands. During May and June, the trades decrease in force and intensity, with increasing ESE winds. As a rule, the winds increase during the morning hours and decrease during the night.

10.2

Typhoons sometimes have occurred over Kosrae Island and

Pohnpei Island, but they are rare during the winter months. Kapingamarangi Atoll is out of the usual path of the typhoons, however, severe storms have occurred on rare occasions.

A region of typhoon development is located N of the Truk Islands. As a rule, such storms do not reach full development until they pass W of Guam. They occur most frequently in late summer or autumn.

10.2 10.2

269

Rain is heavy at Kosrae Island and is fairly evenly distrib-

uted throughout the year. Lelu has an average of 4,850mm and Inshiappu, on the W side of the island, has an average of 6,500mm.

10.2

Pohnpei Island is very wet, rain falling practically every day

from March to December. Twenty-five millimeters of rain falls about 5 days per month. January and February, the so-called dry months, have an excess of 250mm.

10.2

Kapingamarangi Atoll has its heaviest rainfall in May and

June, and then again in October and November; the average rainfall is about 300mm per month. The rainfall is relatively light from February through April, and from July through Sep- tember, the average being about 160mm. In December and January the monthly average is 250mm; most of the rain occurs during storms.

The Mortlock Islands usually have their heaviest rainfall between June and October. Winter and early spring, the so- called dry season, has an average of 160mm or 190mm of rain- fall per month.

10.2 10.2

The Truk Islands average 3,300mm of rain annually. The

rain falls mostly at night, with a maximum during the early morning hours, usually decreasing rapidly after sunrise. Mini- mum rainfall and cloudiness can be expected between 0900 and 1400.

10.2

Tides—Currents.—Currents in the East Caroline Islands

are variable. It is reported that during E winds a strong current, setting N, has been experienced S of Pingelap Atoll. During SE and N winds, a NE current of 1 knot has been reported in this area. An E set occurs at flood tide off the W side of Pingelap Atoll.

An E current has been reported in the vicinity of Ngatik Atoll. The velocity reported is 1.25 to 1.5 knots.

10.2 10.2

The region of the Chuuk Islands lies within the Equatorial

Countercurrent from about March to November. East currents usually predominate during these months. Between December and February, this region lies on or near the N margin of the above countercurrent, so that W currents are usually experi- enced N of the group and E currents S of them.

10.2

The tidal currents are very weak in the East Caroline Islands

and are greatly affected by the ocean currents. As a rule, they are not experienced in the open sea. In the passages leading into the atolls, the tidal currents are strong and turn at about the time of HW and LW.

10.2

The Caroline Islands which occupy a wide expanse of longi-

tude, come in varying degrees under the influence of the Equa- torial Countercurrent, as well as the North Equatorial Current and the South Equatorial Current.

10.2

From June to November, the Equatorial Countercurrent

flows through the whole of the group, with the exception of the Yap Islands and other islands located N of 9°N latitude, in the W part of the group. These lie on or near the boundary between this current and the North Equatorial Current.

10.2

From December to February, the North Equatorial Current

flows through the group N of about 7°N latitude, so that the Republic of Palau and Yap Island lie in the W current while Truk lies on or near the boundary between the two currents. South of about 7°N, the Equatorial Countercurrent is found, with predominant directions varying between NE and SE in different parts of the group.

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