Because of their long fetch distances from near Hawaii into Micronesia, episodes of enhanced Trade Winds generate high surf, which has been known to cause minor coastal inundation. A notable historical inundation on Majuro in December was caused by strong near-gale Trade Winds between that location and Hawaii. The same event caused high surf of 12 to 14 feet even on Guam. Hazardous surf generated by enhanced Trade Winds is typically 3 to 4 meters, and rarely exceeds 5 meters.
Trade winds are a feature of the dry season, and are not typically associated with the occurrence of damaging or severe weather. Enhanced trade winds in regional waters often occur after the passage of a shear line. Shear lines are the southernmost extension of the cold frontal systems associated with mid-latitude cyclones. Shear lines are named for the increase of wind speed that occurs with their passage, with little or no change to the prevailing wind direction.
A band of low clouds is the readily defined signature of a shear line on satellite imagery. These relatively narrow bands of low clouds bring showers for a day or two as they pass through. Rainfall during a shear line passage is often on the order of one-half to one inch, but can be greater if convection forms along the shear line.
During the summer trade winds are less frequent and less intense, and are often replaced by southwest winds when the monsoon trough extends into Micronesia or by tropical cyclones. The monsoon trough is an important feature of the atmospheric circulation pattern of the western North Pacific.
By definition, it is an east-west oriented trough of low pressure, and its axis demarcates a wind shift from easterly winds to its north to westerly or more commonly , southwesterly winds to its south.
The monsoon trough is inherently migratory. As one monsoon trough exits the local region, another often reforms at low latitudes and the cycle repeats. During the summer, a monsoon trough frequently extends into Micronesia.
The southwesterly winds to the south of the monsoon trough axis can reach gale strength, with embedded squall lines containing the highest winds. Sometimes know as monsoon surges, episodes of strong southwest wind may last for more than one week. Monsoon squalls bring sudden white-out rainfall conditions, storm-force wind gusts, and sometimes frequent in-cloud lightning.
The long fetch of the southwesterly winds generates hazardous surf on the western shores of islands and atolls of Micronesia. Large cyclonic disturbances developing in the monsoon trough are known as monsoon depressions. Monsoon depressions are the seed disturbances for nearly two-thirds of the western North Pacific basin tropical cyclones. The average low-level wind flow of the western North Pacific during summer. The monsoon trough extends to near Guam, and the subtropical ridge axis STR stretches across nearly the entire North Pacific at a higher latitude.
ENSO has a substantial effect on the behavior of the monsoon trough in Micronesia. This leads to an enhancement of early season typhoon formation, and an eastward displacement of typhoon formation. At locations in eastern Micronesia e. Low pressure, cyclonic systems originating in the near-equatorial oceans are known as tropical cyclones.
When typhoon intensity cyclones make landfall, the combination of fierce winds, intense rains, and high surf can be devastating e. Most typhoons that strike islands of Micronesia are home-grown.
Beginning as monsoon depressions somewhere in Micronesia, they step through the intensity thresholds and strike islands as depressions, tropical storms, typhoons, or super typhoons.
Occasionally a tropical cyclone which formed in the eastern North Pacific or Hawaiian waters moves west into Micronesia e. Typically typhoons move through Micronesia on a track from east to west. They also tend to gain latitude as they move westward.
Tropical cyclones that form in Micronesia often end up in the Philippines, Taiwan, Japan, or miss land altogether and re-curve into open water on their way to higher latitude.
At these times in the past, groundwater supplies have dwindled to an emergency state, with a major drought disaster declaration in and emergency declarations in [2]. The states of Pohnpei and Chuuk declared drought emergencies on several islands in these states due to food and water shortages from climate variability [6, 7]. In addition, the FSM faces wildfires, extreme tides, sea level variation, and erosion.
Tropical typhoons June to December constitute an annual threat, particularly to the low-lying atolls [1, 3]. With the current stresses on the environment, infrastructure, and economy in the FSM, more frequent extreme events and climate change could pose severe problems for the resilience of the island communities.
To address these issues, several non-profit organizations working with the government have begun to identify marine protected areas and conservation areas to protect resources for food security. In addition, some of the low-lying atolls have made arrangements to secure tracts of land on higher islands for possible relocation.
The many islands are diverse and contain various geographical features, from high mountainous islands, such as Pohnpei, to low-lying atoll islands with scarce land resources, such as Ulithi Atoll. Each of the four states centers around one or more high island, and all but Kosrae include numerous atolls [3]. The total land area is only sq miles sq km , but the nation also covers some 1 million sq miles 2. Chuuk State has a total land area of 49 sq miles sq km and includes seven major volcanic island groups within the Chuuk Lagoon and 24 outer-island atolls — approximately islands total.
Chuuk is the most populous of the FSM states [10]. Pohnpei State is a large state made up of one large volcanic island and six inhabited atolls, with most of its sq miles sq km in Pohnpei Island, the largest island in FSM [3]. Yap State is made up of four large volcanic islands [10], 7 small islands and atolls of which 19 are inhabited , with a total land area of 46 sq miles sq km [3]. Kosrae State, the most easterly state in the country, is essentially one high volcanic island of 42 sq miles sq km [3].
Because of the heavy rainfalls, it has many rivers and waterfalls [10]. Kosrae is the only FSM state without outer islands. Rainfall is relatively high, slightly over inches 5, mm in [5]. The precipitation is normally higher in the highlands. The state has experienced three severe droughts in recent times, in , and Kosrae is located to the south and east of the typhoon track and very rarely experiences a direct strike from a typhoon.
However, Pacific typhoons often go through the development stage in the area, causing severe local winds. During the rainy season of November through March frequent severe rainstorms are sometimes accompanied by damaging winds, which can damage transmission and distribution facilities [9].
By about April, however, the trades begin to weaken, and by July give way to the lighter and more variable winds of the doldrums. Temperature in Chuuk is remarkably uniform; with the highs generally in the middle 80s, and lows in the middle 70s [5]. The northern atolls receive about 80 inches of rainfall a year while the annual rainfall in Southern atolls is normally higher, about inches 4, mm [5].
Although the major typhoon tracks of the western Pacific lie to the north and west of Chuuk, several of the storms have passed close enough to the island to cause widespread damage. Tropical storms generally occur between the months of July and November [9]. Most infrastructure is located close to the coastline, as the interior of the islands are mountainous [4]. Given the frequent rains, the amount of sunshine is never excellent on average, but it is neither too low, in fact, the rains occur in the form of intense but short showers and thunderstorms.
However, the sun tends to be more frequent in the less rainy months. The driest islands are the flat atolls, where there are no hills and mountains which could enhance the formation of thunderclouds: in these cases, precipitation can drop below 4, mm in per year, and in some cases, even below 3, mm in.
However, since the country is affected by the so-called ENSO cycle, the rainfall pattern is quite irregular from year to year. Palikir Here are the average temperatures of the capital, Palikir , located at 7 degrees north latitude, on the island of Pohnpei ex Ponape.
0コメント