Ports.com

HACHINOHE

TROPICAL CYCLONES AFFECTING HACHINOHE

Tropical Cyclone Climatology at Hachinohe

Tropical cyclones which affect Japan generally form in the area bounded by 5°N to 30°N and 120°E to 165°E. The latitudinal boundaries shift poleward during the summer months and then equatorward in winter in response to the seasonal changes of the synoptic environment. Although affected by tropical cyclone activity, Hachinohe is well north of the latitudes where tropical cyclones most frequently occur and are the strongest. Also, because of Hachinohe's high latitude, many of the storms become extratropical by the time they enter the 180 nmi threat radius. Consequently, although the port is exposed and vulnerable to strong winds whatever the cause, the effects of tropical cyclone activity at Hachinohe are routinely less frequent and mostly less intense than that observed at more southerly locations in Japan.

For the purpose of this study, any tropical storm or typhoon approaching within 180 nmi of Hachinohe is considered to represent a threat to the port. Table V-35 contains a descriptive history of all tropical storms and typhoons passing within 180 nmi of Hachinohe during the 47-year period 1945-1991. All of the tropical cyclone statistics used in this report for storms passing within 180 nmi of Hachinohe are based on the SAIC generated data set used to compile Table V-35.

Because no observational records are available for Hachinohe, all observational data cited in this report are based on official weather observations recorded at Misawa, which is located approximately 11 nmi north-northwest of Hachinohe.

The primary tropical cyclone season for Hachinohe is from August through October, although historically they have occurred in all months in the genesis area described in a preceding paragraph. As shown in Table V-36, no tropical cyclones passed within 180 nmi of Hachinohe prior to June or during November in any year since 1945. Two have occurred in each of the months of June and July, and 1 occurred in December. Of the 55 storms occurring during the 47-year period, only 6 were of typhoon intensity (64 kt) at CPA. The table also shows the motion history of the storms. The average heading and speed of tropical storms and typhoons passing within 180 nmi of Hachinohe during the 47-year period was 042° at 34 kt at CPA. The average storm speed during October is a high 44 kt.

The storm speeds given in Table V-36 are relatively high when compared to "normal" movement speeds for tropical cyclones, and are due to the northerly location of Hachinohe. By the time the storms reach the 180 nmi threat radius, they are usually being influenced by upper-level westerly flow and accelerating to the northeast.

During the 47-year period 1945 through 1991, there were 55 tropical storms and typhoons that met the 180 nmi threat criterion for Hachinohe, an average of just over 1 per year. Figure V-147 shows the monthly distribution of the 55 storms by 7-day periods. As the figure shows, the period of peak activity is from early August through September. Of the 5 storms that were still classified as typhoons while at CPA, 4 occurred during September, and 1 in October.

Figure V-148 shows the annual distribution of tropical storms and typhoons passing within 180 nmi of Hachinohe during the 47-year period 1945 through 1991. During the 20-year period 1948 through 1967 there were no years without at least one tropical cyclone passing within 180 nmi. For several years in the 1970's and 1980's no tropical storms or typhoons passed within the 180 nmi threat radius.

Figure V-149 presents a graphical depiction of the number of tropical cyclones versus CPA. The storm classification is based on the maximum wind near the storm center while that center was within 180 nmi of Hachinohe, not necessarily at CPA. The sloping lines represent mathematical fits to the data points for the various intensity classifications. The average radii of maximum wind for 34, 100, and 140 kt tropical cyclones at Hachinohe are 35.4, 33.8, and 30.9 nmi, respectively.

Figure V-150 depicts, on an 8-point compass, the octants from which the 55 tropical cyclones in the data set approached Hachinohe. The majority of the storms, 35 of 55 (63.6%), approached Hachinohe from the southwest octant, with the remainder, 20 of 55 (36.4%), equally split between the west and south octants. It should be noted that the approach direction is determined at CPA, and may not represent the initial approach direction of the tropical storm or typhoon toward Hachinohe.

Figures V-151 and V-152 provide information on the probability of remote tropical storms and/or typhoons passing within 180 nmi of Hachinohe and average time to CPA. The solid lines represent a 'percent threat' for any tropical cyclone location within the area depicted. The heavy dashed lines represent the approximate time in days for a system to reach Hachinohe. For example, in Figure V-151, during the months of July and August, a tropical cyclone located at 25°N 135°E has approximately a 10% probability of passing within 180 nmi of Hachinohe and would reach Hachinohe in about 3 to 4 days.

There is a minor difference in threat axis orientation southwest of Hachinohe on the preceding two figures, but the most significant difference in the figures is the threat axis orientation south of Japan. The axis extends south of central Honshu to about 30°N before turning southeastward to the more tropical latitudes during July and August, while the threat axis for the other months continues a southwestward orientation south of Japan before finally turning southeastward south of 25°N.

Wind and Topographical Effects

The harbor is exposed and vulnerable to wind. Winds from the western semicircle prevail during the autumn and winter seasons, with the strongest normally being post-frontal winds associated with extra-tropical low pressure systems. Some of the effects of westerly winds are diminished by the hills near the port and, to a limited degree, by the northern extension of the Japanese Alps. Winds from the eastern semicircle are another matter, however, and reach the port with their full open-ocean strength.

Prevailing winds at the port vary by season (Table V-37). Wind measurements for the port are taken near the mouth of the Niida River at the weather station (Fig. V-146B). Elevation of the wind equipment is about 66 ft (20 m) above sea level, and considered to be representative of winds in the port area. Typhoons affect the local area but are relatively infrequent occurrences; the port is affected primarily by strong extratropical weather systems. Port personnel state that winds to 70 kt (35 m/s) were observed when Typhoon Kinna passed in September 1991. The strong winds were forecast, and large ships left the port to evade at sea rather than remain in port.

Local harbor personnel state that the most hazardous winds for the port area are caused by a migratory extra-tropical double low pressure system, with centers over the Sea of Japan and over the Pacific Ocean east of Japan. The double-low configuration apparently causes the easternmost of the two lows to move northward close along the coast of Honshu, and then intensify as the low in the Sea of Japan merges with the easternmost low. The scenario brings strong winds and high seas from the northeast quadrant to Hachinohe--the worst situation for the port.

Local Weather Conditions

The data contained in Table V-38 has been selected from observations recorded at Misawa (11 nmi north-northwest of Hachinohe), the closest official recording station to the port.

A total of 55 tropical storms or typhoons passed within 180 nmi of Hachinohe during the period 1945 through 1991. Of that total, 21 (38%) caused winds of 22 kt at Misawa, the nearest observation station to the port (11 nmi north-northwest), and only 3 (5%) caused winds of gale force (34 kt). The direction of passage made little difference in the observed winds, as 10 (48%) of the 21 storms causing winds of 22 kt passed to the west and 11 (52%) passed to the east.

The basic difference between an east passage and a west passage is the direction of the resultant wind. If the tropical cyclone passes to the west of Hachinohe, the winds will generally have a strong southerly component. An example of this is Typhoon Nancy in 1961. Passing 71 nmi west-northwest of the port, Nancy caused sustained west-southwesterly winds of 38 kt at Misawa, with gusts to 54 kt.

If the tropical cyclone passes east of Hachinohe, the path will be over water and the winds at the port will be generally northerly. An example was Typhoon Owen in 1979, which brought sustained north-northwesterly winds of 33 kt with gusts to 42 kt to Misawa.

The track segments in Figure V-153 reflect the tropical cyclone positions when sustained winds of 22 kt were being experienced at Hachinohe (Misawa). Only 21 of the 55 storms that passed within 180 nmi during the period of 1945 through 1991 resulted in sustained winds of 22 kt at Hachinohe (Misawa). Figure V-154 shows the positions of the centers of the 3 tropical cyclones that caused sustained winds 34 kt at Hachinohe (Misawa).

Wave Action

As discussed in section location and topography, without the extensive grid of breakwaters the port of Hachinohe would be exposed and vulnerable to open ocean wave motion. Even with the breakwater system, some portions of the port still experience wave motion that passes through the harbor entrance between the breakwaters.

The port has observed 20 ft (6.09 m) waves outside of the breakwater system during strong winds from the eastern semicircle. Although the waves impact the breakwaters with great force, the breakwater system allows only a portion of the wave energy to pass into the inner harbor. When the highest waves are observed outside the breakwaters, the waves in the inner harbor are limited to 5 to 7 ft (1.5 to 2 m).

The berths that are most likely to be utilized by U.S. Navy vessels, berth 1-E and the fuel piers, are in well protected locations. Berth 1-E could experience waves of 5 to 7 ft from a strong easterly wind, but the waves would be parallel to the ship's longitudinal axis and should not pose a problem to the moored ship. Because of its location on the south side of a large filled-in land area, waves at the fuel piers would likely be limited to chop from wind waves.

Source: http://www.nrlmry.navy.mil/port_studies/thh-nc/japan/hachinoh/text/sect4.htm