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OMINATO

THE DECISION TO EVADE OR REMAIN IN PORT

General

The exposure of the port facilities at Ominato to the effects of wind precludes any decision to remain in the port during a strong wind event. This conclusion is applicable to all locations. Although wave motion is relatively benign in many wind situations, there is no protection from wind.

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-190 and V-191, discussed earlier, address the probability of existing tropical cyclones later affecting Ominato. Figures V-194 and V-195 have been prepared as additional aids for the commander to use when evaluating a given situation. In contrast to Figures V-190 and V-191, Figures V-194 and V-195 consider only those storms which later passed within 180 nmi of Ominato. 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 Ominato is concerned. It must be stressed that the other 50% of the storms which later affect Ominato will be outside of these bounds. Another important factor is that the actual JTWC forecast will always take precedence over the tracks and translational storm speeds suggested by Figures V-194 and V-195.

With the above restrictions in mind, the following time/action sequence aids, to be used in conjunction with Figures V-194 and V-195, are provided.

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

a. Review material condition of ship.

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

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 Ominato (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 Ominato.

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 Ominato area:

a. Sortie from the harbor and Mutsu Bay, 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-190 and V-191 (tropical cyclone threat axes and approach times to Ominato). In all cases, Optimum Track Ship Routing (OTSR) should be consulted as to the best evasion route.

Two basic evasion routes are available: (1) exiting Mutsu Bay and moving west through Tsugaru Strait into the Sea of Japan, and (2) exiting Mutsu Bay and moving east through Tsugaru Strait into the Pacific Ocean 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 Mutsu Bay, moving into in the Sea of Japan would keep the vessel on the weaker, left side of the storm's circulation and avoid 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 Mutsu Bay, moving through Tsugaru Strait into the Pacific Ocean and proceeding south 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 strong winds of the storm's dangerous semicircle. In a best case situation, depending on the size of the storm's circulation the ship may still be liable to encounter strong southerly winds along the coast. 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 40 nmi from Ominato to the open waters of Tsugaru Strait, and another 50 nmi to the east coast of Honshu. At a steaming speed of 20 kt, it will take approximately 4 to 5 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 150 miles (or more) closer to Ominato by the time the east coast of Honshu is reached. It should be noted that the average speed of movement of tropical cyclones occurring during the 48-year period 1945-1992 is 35 kt when at CPA to Ominato (Table V-45). Those occurring during September average a relatively rapid 38 kt, so many storms will move faster. Six of the storms listed in Table V-45 have speeds in excess of 50 kt when at CPA to Ominato and one, tropical storm Tip in October 1979, had a forward speed of over 73 kt.

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 Ominato 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/ominato/text/sect6.htm