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Sector 10. Micronesia, Palau, and Guam

10.54 Tobi Island (3°00'22"N., 131°07'26"E.) is covered

with coconut palms. A cultivated area is situated near the middle of the island. Most of the houses are situated on the SW side of the island. A dispensary and radio station are situated on the island.

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The island is fringed by a reef, which at the N end, extends

nearly 0.5 mile NE. A dredged channel has been reported to have been cut through the reef fringing the SW side of the island.

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A SE current with a velocity of 1.25 knots has been reported

in the vicinity of the island. Tobi lies in the flow of the Equa- torial Countercurrent throughout the year.

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Some piers and mooring buoys are reported to be situated on

the SW side of the island. It was reported that a medium-size vessel has berthed at one of the piers.

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Helen Reef (2°55'N., 131°48'E.) is an atoll reef enclosing a

lagoon. The reef, on which the seas break heavily, is usually dry at LW. Helen Island, densely wooded, is located near the N end of the reef. The island has a whale-like appearance when viewed from the NNE.

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A channel, with a 4.6m shoal in the fairway, leads into the

lagoon from near the middle of the W side of the reef. At HW, when the sea is smooth, there are sometimes no breakers on the reef so that caution is necessary when making the approach. The tidal currents setting over Helen Reef are strong. When

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the tide is falling, the water flows out of the lagoon and over the reef in all directions until the reef is uncovered, and then flows out through the channel on the W side. On the rising tide, a reverse effect is noted. Toward the end of the ebb and at the beginning of the flood, the tidal currents in the channel are strong, but as only few parts of the reef completely dry, the maximum velocity does not exceed 1.8 knots.

Guam

10.55 Guam, a U.S. Territory since 1898, is not included in

the Commonwealth of the Northern Marina Islands, which ex- tends from Rota (14°19'N., 145°12'E.) to Farallon de Pajaros. The Northern Mariana Islands became a self-governing Com- monwealth in political union with, and under the sovereignty of, the United States on 3 November 1986. Refer U.S. Coast Pilot 7 for further information on the Mariana Islands. Guam, the southernmost and largest in the chain of islands of

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the Mariana Archipelago, is about 30 miles long and varies from 4 to 8 miles in width.

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The N end of the island is a plateau of rolling hills set on ver-

tical cliffs rising about 150m above sea level. The S end of the island consists of high volcanic hills. The plateau is covered with a thick growth of jungle; the volcanic hills support mainly sword grass. The highest hills are found in the W central and S parts of the island.

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The capital of Guam is Agana; the chief port is Apra Harbor. Surface, subsurface, and aircraft operations including firing

exercises are conducted at various times in areas within an approximate 220 mile radius of Guam.

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Winds—Weather.—The islands of the Marianas Archipe-

lago have similar weather conditions. Under ordinary circum- stances, the wind and seas in the vicinity of Guam are E due to the Northeast Trades. West winds are at times experienced during the summer months as Guam is barely within the limits

289

of the Southwest Monsoon. These winds are light as a rule. In the vicinity of Guam, NE and ENE winds prevail for 6 months of the year. These winds blow from the NE to E 65 per cent of the time between December and May, and are strongest during these months. Between June and November, the surface winds are quite variable; calms are rare. In the S islands, the winds show a slight S trend as early as May.

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In Guam, the average mean temperature is 27°C, the mean

maximum is 32°C, and the mean minimum is 21°C The temp- eratures for the rest of the Mariana Islands are quite uniform throughout the year. January and February are the coolest months. The nights are cooler in the N islands. Temperatures above 31°C normally occur from 13 to 22 days a month be- tween April and August. The daily minimums seldom fall below 23°C during the summer months. The yearly range of temperatures is 16°C in the S and 14°C in the North. The daily range is about 12°C.

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Humidity is high throughout the year, but there is somewhat

less humidity from December through May. The yearly average is about 76 per cent, the January average is 68 per cent, and the June average is 84 per cent.

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Fog and mist are rarely reported in the Guam-Saipan-Tinian

areas. Visibility of less than 1.25 miles can be expected on less than 1 day per month.

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The yearly average cloud cover is about 0.7. The maximum

coverage of 0.8 to 0.9 occurs during the summer months (July to October). Cloudiness is higher over the islands than over the adjacent seas. Clouds are more frequent during the daytime. Tides—Currents.—Currents in the vicinity of the Mariana

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Islands are W. They are strongest near to and S of Saipan Is- land, and gradually become weaker N of that island. In June, the Equatorial Drift Current was reported to be strongest dur- ing that season at 13°N and to run to the NW at a maximum rate of 1 knot.

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Variable currents are sometimes encountered near the is-

lands. These are caused by the physical makeup of the island and by the additional force of the tidal currents.

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An almost constant SW set has been reported along the NW

coast of Guam during the Northeast Trades. This current has been felt up to 10 miles offshore.

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Regulations.—See the NOS Coast Pilots and the chart for

regulations pertaining to navigation within U.S. waters. Addi- tional regulations will be cited in the text where appropriate.

10.56 Guam (13°25'N., 144°44'E.) is the southernmost, lar-

gest, and most populous island of the Mariana Archipelago. Guam is a territory of the United States and exercises local self-government under the U.S. Department of Interior. Aspect.—Guam is reef-fringed, which dries in spots, over a

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greater part of its shoreline. From a distance the island appears flat and even; its E side is bordered by steep cliffs.

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The S part of the island is mountainous, with the highest

peaks being Mount Lamlam, 407m high, and Jumullong Man- glo, with a height of 391m, lying 5.5 miles NNW of the S end. In the central range are Mount Tenjo, 311m high, about 5.8 miles NNE of Jumullong Manglo. Mount Alutom, about 1 mile NNE of Mount Tenjo, 330m high, and Mount Chachao, close N of Mount Alutom, 318m high, are the highest peaks in that range.

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The N part of the island is comparatively low.

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