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OTARU

THE DECISION TO EVADE OR REMAIN IN PORT

General

The exposure and orientation of the Port of Otaru effectively precludes any decision to remain in the harbor during the passage of a tropical cyclone. As discussed in Sections 12.4 and 12.5, the harbor is exposed and vulnerable to wind and waves. Evasion is considered to be the only reasonable option when Otaru is threatened by a tropical cyclone. According to local harbor authorities, ships that have remained in the inner harbor during past strong northeasterly wind events have had 3-1/2 inch (90 mm) mooring lines part due to wind stress. One vessel parted nine lines during a single wind event.

Evasion Rationale

It is of utmost importance that the commander recognize the inherent dangers that exist when his/her ship is exposed to the possibility of hazardous weather. Proper utilization of meteorological products, especially the Naval Pacific Meteorology and Oceanography Center West/Joint Typhoon Warning Center (NPMOCW/JTWC) Guam tropical cyclone warnings, and a basic understanding of weather will enable the commander to act in the best interest of the unit, and complete the mission when the unfavorable weather subsides.

Figures V-164 and V-165, discussed earlier, address the probability of existing tropical cyclones later affecting Otaru. Figures V-168 and V-169 have been prepared as additional aids for the commander to use when evaluating a given situation. In contrast to Figures V-164 and V-165, Figures V-168 and V-169 consider only those storms which later passed within 180 nmi of Otaru. Approximately 50% of these storms are contained within the bounds shown by the arrow. Thus, the arrow and the associated timing arcs can be considered as an average approach scenario insofar as Otaru is concerned. It must be stressed that the other 50% of the storms which later affect Otaru will be outside of these bounds. Another important factor is that the actual NPMOCW/ JTWC forecast will always take precedence over the tracks and translational storm speeds suggested by Figures V-168 and V-169.

The relative distance between the time arcs, coupled with the orientation of the broad arrows, is indicative of the acceleration of tropical cyclones following recurvature. The typical rapid rate of approach to the Otaru area during the last 24 to 48 hours must be considered in all situation analyses.

With the aforementioned restrictions in mind, the following time/action sequence aids, to be used in conjunction with Figures V-168 and V-169, are provided.

I. An existing tropical cyclone moves into or development takes place in Area A with long range forecast toward Otaru:

a Review material condition of ship.

b. Formulate plans for expeditious sortie from the harbor and evasion route to be taken in the event the tropical cyclone threatens Otaru.

c. Reconsider any maintenance that would render the ship incapable of getting under way, if need be, within 48 hours.

d. Plot NPMOCW/JTWC Guam warnings when received and construct the danger area. Reconstruct the danger area for each new warning.

II. Tropical cyclone enters Area B with forecast movement toward Otaru (recall that tropical cyclones tend to accelerate rapidly after recurvature).

a. Reconsider any maintenance that would render the ship incapable of getting underway, if need be, within 24 hours.

b. Finalize plans for expeditious sortie from the harbor and evasion route to be taken in the event the tropical cyclone threatens Otaru.

c. Plot NPMOCW/JTWC Guam warnings when received and construct the danger area. Reconstruct the danger area for each new warning.

III. Tropical cyclone has entered Area C and is moving toward the Otaru area:

a. Sortie from the harbor, taking an evasion route that will allow the unit to encounter the most favorable weather conditions during the passage of the tropical cyclone.

b. Plot NPMOCW/JTWC Guam warnings when received and construct the danger area. Reconstruct the danger area for each new warning until the storm threat has passed.

Evasion at Sea

Evasion routes at sea may be developed by using NPMOCW/JTWC tropical cyclone warnings, and Appendix A (Bi-Weekly Tropical Storm and Typhoon Tracks for the Western North Pacific Ocean) for the period of interest. They should be used in conjunction with Figures V-164 and V-165 (tropical cyclone threat axes and approach times to Otaru). In all cases, Optimum Track Ship Routing (OTSR) should be consulted as to the best evasion route.

Two basic evasion routes are available: (1) remaining in the Sea of Japan, and (2) exiting the Sea of Japan through the Tsugaru Strait (between Hokkaido and Honshu) and proceeding south along the east coast of Honshu. If the tropical cyclone is moving northeastward on a track that would take it east of Otaru, remaining in the Sea of Japan would keep the vessel on the weaker, left side of the storm's circulation thereby avoiding the strongest winds of the storm. However, the ship may be exposed to relatively strong winds from the northwest quadrant as the storm passes and high pressure moves into the Sea of Japan behind the storm's circulation.

If the storm is forecast to pass west of Otaru, moving through the Tsugaru Strait into the Pacific Ocean along the east coast of Honshu should be considered. It must be emphasized that this option has a potentially serious drawback; if the tropical cyclone should move east of the forecast track, and therefore closer to the ship's evasion route, the ship may encounter the strongest winds of the storm's dangerous semicircle. Any tropical cyclone moving northeastward across the Sea of Japan may have a circulation large enough to bring strong southerly winds to the coastal waters east of northern Honshu. However, the winds should be short-lived because of the historically rapid movement of tropical cyclones when they reach the latitudes of northern Japan.

Regardless of the option chosen, it is of utmost importance to begin the sortie as early as possible. It is approximately 175 nmi from Otaru to the west entrance to Tsugaru Strait, and another 75 nmi to the east coast of Honshu. At a steaming speed of 20 kt, it will take approximately 12 to 13 hours to complete the transit. If the tropical cyclone has recurved before the sortie is commenced and is moving at 30 kt, the storm could be 360 miles closer by the time a sortieing vessel reaches the east coast of Honshu. It should be noted that the average speed of movement of tropical cyclones occurring during the period 1945-1992 is 34 kt when at CPA to Otaru (Table V-40), while September storms average an even faster 38 kt. Table V-39 lists four storms that were moving at over 50 kt when at CPA to Otaru.

It must be remembered that tropical cyclones are notoriously difficult to accurately forecast, especially in the recurvature phase; the 48-hour forecast position error may exceed 200 nmi. A storm may be closer to or farther from Otaru than the forecast indicates, or right or left of the storm's forecast track. Each tropical storm or typhoon must be considered as differing from those preceding it. The accompanying synoptic situation must be fully understood. To blindly establish and follow only one technique or rule for avoiding a storm's danger area is not prudent and, in fact, may ultimately place the ship in harm's way.

Source: http://www.nrlmry.navy.mil/port_studies/thh-nc/japan/otaru/text/sect6.htm