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Marine Meteorology: Koper - Capodistria

Port Information

Geographic Location

Coordinates: 45°33'North 13°44'East
The Port of Koper, Slovenia is situated at the head of Koprski Bay, which is entered between Debeli Point (45°35'N 13°42'E) and Petelinji Point (45°32'N 13°39'E). The city of Koper (once known as Capodistria) is located on the southeast coast of Koprski Bay. Koper is located west of a valley that passes between mountainous terrain lying east of Debeli Point, and the mountainous terrain lying south and east of Petelinji Point. The better known city of Trieste, Italy is located approximately 6 nmi (11 km) north of Koper.
Anchorage can be made at several locations near the western edge of Koprski Bay. Selection of the anchorage to be used is dependent on wind direction and speed.

Harbor As Haven

As of the June 1998 port visit the Port of Koper was undergoing extensive development that would enlarge the port facilities and realign the port configuration. The port is comprised of three basins.

Basin 1 is the southernmost of the three, and is used for general cargo purposes. Seven primary berths are identified around the perimeter of the basin. A Fleet Landing is established in Basin 1 whenever U.S. Navy ships are anchored in Koprski Bay. Pier 1 in Basin 1 is the recommended location.

Basin 2 lies just north of Basin 1. It is used primarily for bulk cargo and as an oil terminal. All petroleum product tankers go to Basin 2.

Basin 3 is the northernmost of the three basins. It has RO-RO facilities on its eastern end. The south side of the basin is used primarily for the loading and unloading of bulk materials, including iron ore and coal.
The berths in the three basins are oriented east-west, so onsetting and offsetting forces of Bora winds are minimized. Under-keel clearances of 3.3 to 6.6 ft (1 to 2 m) are required..
All anchorages in Koprski Bay are exposed to winds from west through north. Charted depths in all locations range from 59 to 66 ft (18 to 20 m). Local authorities state that holding in Koprski Bay is good, but Mediterranean Pilot states that holding is not good on a bottom of soft yellow mud or sand. Mediterranean Pilot further states that "mariners are advised to consider carefully weather conditions when anchoring" in Koprski Bay.
The Port of Koper experiences frequent Bora wind events. The traditional Bora is a wind whose source is so cold that when the air reaches the coast, the dynamic warming caused by subsidence is insufficient to raise the air temperature to the level normally experienced. The Bora occurs when cold air accumulates over the Balkan Peninsula to the extent that it spills over coastal maintain ranges and "falls" down the steep slopes to the sea. Due to topography differences, Bora winds at Koper are not as strong as those experienced at Trieste. Nevertheless, sustained wind speeds of 54 kt (100 kph) have been observed at the Port. Bora events may last two to three days. There are two types of Boras, known as "White (anticyclonic) Bora" and "Black (cyclonic) Bora." The White Bora results when a strong pressure gradient exists between a cold high pressure area north of Slovenia and a low-pressure area over the Mediterranean Sea. The White Bora is characterized by cold, clear weather. The so-called Black Bora results when the low-pressure area is located over the Adriatic Sea resulting in cloudy and rainy weather over Slovenia. Due to the instability of the cold air mass, winds in a White Bora are gustier than those in a Black Bora. The gusts can be more than twice the sustained wind speed. The direction of the wind from either Bora is approximately 060° in the entrance channel (30° off the port bow of an incoming vessel) and in Basin 3, the worst affected area of the port. The direction becomes somewhat more easterly in the southern parts of the harbor, including Basins 1 and 2. Bora events are normally strongest and most frequent during the months of December through March, but can occur outside that four-month period. They are uncommon during the summer season, but weak Boras of short duration may occur. Bora winds do not normally cause problems for ships in port, but additional mooring lines are deployed when necessary to keep a ship safe at her berth. The safest anchorage during a Bora is located in Koprski Bay just south of Debeli Point.
Koper is also affected by other wind events, including Scirocco, Jugo, and Maistral. Scirocco wind directions vary from southeast to south-southwest and may last for several days. The winds are more-or-less perpendicular to the orientation of the entrance channel and cause control problems for ships entering or leaving port. Sustained Scirocco winds can raise seas of 6.6 to 9.8 ft (2 to 3 m) in the open water west of Koper, but waves in the harbor are fetch limited by the land mass south of Koprski Bay. Consequently, waves in the harbor are not a problem. Departing vessels up to 1,500 GWT often anchor in Piranski Bay approximately 8 nmi west-southwest of the Port of Koper to wait until Scirocco conditions abate over the open waters of the Adriatic Sea. When strong southerly Scirocco winds prevail, a location just northeast of Petelinji Point is recommended as an anchorage at Koper.
Jugo winds are southwesterlies, and also pose control problems for ships in the entrance channel. A location in Koprski Bay approximately midway between Debeli Point and Petelinji Point is the preferred anchorage during southwesterly Jugo winds.
Maistral is a seasonal northwesterly wind that is prominent during the months of May through September. The Maistral commonly occurs between late morning and 5 or 6 pm, the normal hours of a sea breeze. Maistral wind speeds are usually in the 11-16 kt range.
Local forecasting rules:

Bora winds will onset approximately 3-4 hours after "cap clouds" develop over the mountains east of Koper.

A Scirocco is forthcoming if the water level in the harbor is higher than normal.

A change in weather can be expected if the Maistral is not blowing by 1000L.
Forecast availability:

The Hydrometeorological Institute of Slovenia maintains a web page on the Internet for dissemination of weather forecast information. At the time of this writing, everything is displayed in Slovenian. However, an English language version is under development, with completion anticipated in 1999. The URL for the Hydrometeorological site is: https://www.rzs-hm.si
Planned content for the Internet site includes:
24 and 48 hour graphical forecasts for Slovenia and surrounding territory
Graphical-textual English forecast for maritime regions
Products of LAM (approximately 800 x 800 km, resolution approximately 10 km)
Precipitation fields (+48 hours, every 6 hours)
Surface wind fields (+48 hours, every 6 hours)
850hPa wind fields (+48 hours, every 6 hours)
Cloudiness (+48 hours, every 6 hours)
Surface wind fields (for maritime region, resolution approximately 2.5 km)
Alphanumerical observations from surface stations (synoptic and automatic)

The above information is already available on the Internet site, but only in Slovenian.

If specific forecast information is required before the English language version is available on the Internet, faxed forecasts can be requested from the Hydrometeorological Institute at telephone number ++386 61 327 461 (ask for forecasters). A direct number for obtaining telephone consultations with an operational forecaster may also be obtained by calling the aforementioned number.

Currents and Tides

There is a large counterclockwise current gyre in the center of the Adriatic Sea. The large gyre sometimes breaks into two smaller gyres. In both scenarios, the general current flow is northward along the eastern shores of the Adriatic Sea and southward along the western shores.
A north-setting current with a maximum speed of approximately 1 kt may be observed along the coastal waters west of Koprski Bay. In Basin 2 of the Port of Koper, precipitation runoff at the mouth of the Rizana River may generate westerly flowing currents of 6 to 7 kt during periods of heavy rain.
Tidal fluctuation in Koprski Bay and the Port of Koper is approximately 3 ft (90 cm).

Visibility

Visibility is generally good at Koper. During a white Bora, the winds bring dry, clean air that can persist for days at a time.
Koper is not far from major sources of fog, including the Po Valley and the Gulf of Venice. It is not uncommon for westerly winds to advect fog from either area to Koper. On average, fog occurs on five to 10 days per year at Koper, with December having more foggy days than other months.
During periods of reduced visibility, a ship may not depart the harbor until visibility improves to at least twice the vessel's length.

Hazardous Conditions

Spring

The spring season over the northern Adriatic Sea, including Koper, extends from March through May. It is noted for periods of stormy, winter-type weather that alternate with false starts of settled summer-type weather. Conditions moderate as the season progresses.
Some visibility restrictions can occur with fog in the early spring. This is usually due to a fog-laden west wind.
Wind chill is a factor to be considered for personnel working in exposed, outdoor locations during early spring. When indicated, the Wind Chill Table [see https://www.nrlmry.navy.mil/~cannon/medports/Koper/windchilltable.html] should be used to determine the equivalent wind chill temperature for specific air temperature and wind speed combinations.

Summer

The summer season extends from June through September. Summer weather in the northern Adriatic Sea is generally warm and dry with light winds. Strong Bora events are uncommon. The mild weather results from the great continental low pressure area that replaces the Eurasian winter anticyclone. The low is centered over southwest Asia, with an extension westward over Asia Minor.
Thunderstorms are most frequent during the summer, but only average three or four times per year. The storms occasionally form over the coastal terrain and move over the port area. Thunderstorms normally last only 2 to 4 hours in the Koper area.

Autumn

The autumn season is short, usually lasting about the month of October. The season is characterized by an abrupt change to winter-type weather.
Wind chill for personnel working in exposed, outdoor locations is normally not a factor until after October. When indicated, the Wind Chill Table [see https://www.nrlmry.navy.mil/~cannon/medports/Koper/windchilltable.html] should be used to determine the equivalent wind chill temperature for specific air temperature and wind speed combinations.
Thunderstorms are most frequent during the summer, but may occur during autumn. The storms occasionally form over the coastal terrain and move over the port area. One strong November thunderstorm caused northerly "Tramontana" winds of 108 kt (200 kph) at Koper. Thunderstorms normally last only 2 to 4 hours in the Koper area.

Winter

Winter usually lasts for the months of November through February. A great continental anticyclone over Eurasia develops and extends southwestward toward the Balkans. Cold Bora winds and clear weather (a white Bora) usually result with this weather pattern as transient extratropical low pressure systems over the Mediterranean Sea cause strong pressure gradients to develop over the Adriatic region on the south side of the anticyclone. Stormy and unsettled weather at Koper may accompany the Bora (a black Bora) when the low-pressure systems move across the Adriatic Sea rather than farther south over the Mediterranean Sea.
Thunderstorms are most frequent during the summer, but are possible all year. They occasionally form over the coastal terrain and move over the port area. A strong November thunderstorm caused a northerly "Tramontana" wind gust of 108 kt (200 kph) at Koper. Thunderstorms normally last only 2 to 4 hours in the Koper area.
Wind chill must be taken into consideration when work is being performed in exposed, outdoor locations during the winter season. The Wind Chill Table [see https://www.nrlmry.navy.mil/~cannon/medports/Koper/windchilltable.html] should be used to determine the equivalent wind chill temperature for specific air temperature and wind speed combinations.

Protective or Mitigating Measures

Moving to a New Anchorage

Because Koprski Bay is protected from most hazardous wave motion, wind will be the dominating weather factor for ships anchored in Koprski Bay or moored alongside berths in the Port of Koper. Waves generated by Scirocco and Jugo winds do not reach the port due to the protection afforded by the land mass south of Koprski Bay. Bora winds blow seaward and do not have enough fetch to generate bothersome wave heights in Koprski Bay. During an intense Bora event, ships moored alongside a berth should add lines to prevent excessive ship movement. Anchored vessels, especially those that are empty, have large sail areas, or do not have enough chain to provide an adequate scope of anchor chain, should sortie from the port because of the danger of anchor dragging. If remaining at anchor, vessels should deploy an adequate scope of chain to provide maximum holding strength on the mud bottom. Steaming to the anchor during the strongest winds may be required.
Positioning a vessel in the lee of high terrain as close to the coastline as possible will decrease the effect of the local seas during a severe Bora. Territorial limits of the various countries bordering the Adriatic Sea may prohibit taking maximum advantage of this option, however. The evaluation of Trieste, Italy recommends a location north of Castella Miramare, Italy, moving to within one-half mile of the coast. This maneuver will decrease seas substantially and decrease winds slightly. Since there are mussel farms in this area, up-to-date navigation charts must be consulted before exercising this option.

Sortie/Remain in Port

There is no sortie information available for this port. The position of Koper in the extreme northern part of the Adriatic Sea severely limits sortie options.

Scheduling

There is no scheduling information available for this port.

Harbor Protection

Wind and Weather:

The Port of Koper is vulnerable to frequent Bora wind events. During late autumn, winter and early spring, in extreme events the cold Bora winds can reach sustained velocities of 54 kt (100 kph), with doubling of gust velocities. Some Bora events last two to three days. Although Bora winds do not normally cause problems for ships in port (most berths are oriented east-west), additional mooring lines may be required to keep a ship safely alongside her berth. Bora winds are felt most strongly in Basin 3 and in the entrance channel. The typical Bora wind direction is approximately 060° in Basin 3 and in the channel, but more easterly in Basins 1 and 2. Bora winds are most commonly observed in the December through March period, but they can occur during other months.

Boras are classified locally as being a "White Bora" or a "Black Bora." A White Bora results when a strong pressure gradient exists between a cold high pressure area north of Slovenia and a low pressure area over the Mediterranean Sea. A White Bora is characterized by cold, clear weather and very gusty winds. A Black Bora results when the low pressure area is located over the Adriatic Sea so that the weather over Slovenia is cloudy and rainy. Black Bora winds are less gusty than those in a White Bora.

Anchor dragging is possible during a strong Bora event. Those vessels opting to remain at anchor at Koper should deploy enough scope of chain to provide maximum holding strength on the mud bottom. Steaming to the anchor may be required to prevent anchor dragging during the strongest winds. Positioning a vessel in the lee of high terrain as close to the coastline as possible will decrease the effect of the local seas during a Bora event.

Koper is also affected by other wind events, including Scirocco, Jugo and Maistral. Scirocco directions vary from southeast to south-southwest. Because of their direction being more-or-less perpendicular to the channel orientation, they can cause handling problems for ships in the channel. When Scirocco conditions prevail, a location just northeast of Petelinji Point is recommended as an anchorage at Koper. Jugo winds are southwesterlies, and also cause handling problems for ships in the channel. An anchorage in Koprski Bay approximately midway between Debeli Point and Petelinji Point is the recommended anchorage when Jugo winds occur. The Maistral is a northwesterly wind that occurs during the warm months of late spring, summer and early autumn. Maistral speeds are usually in the 11-16 kt range, so they pose little problem to vessels at the Port of Koper.

Thunderstorms are possible at Koper year-round, but are most frequent during summer. Such storms can be intense, with one strong November storm causing a northerly "Tramontana" wind gust of 108 kt (200 kph) at Koper.
Waves:

Due to limited fetch, Bora winds do not raise problem waves at the Port of Koper. A sustained southerly or south-southwesterly Scirocco event can raise seas of 6.6 to 9.8 ft (2 to 3 m) in the open water west of Koper, but waves in Koprski Bay are fetch limited by the land mass south of the bay. When such conditions occur, departing vessels up to 1,500 GWT often anchor in Piranski Bay to wait until the winds and waves over the Adriatic Sea abate. Piranski Bay is located approximately 8 nmi west-southwest of the Port of Koper.

Local Hazardous Weather Conditions

Wind and Weather: Koper's climate is dominated by the Bora wind, which can occur anytime during the year. However, the peak frequency occurs in the cold season (November - March). To a lesser extent, the Scirocco wind affects Koper but is not nearly as strong or as frequent as the Bora. Gulf of Genoa lows have an influence on weather in the northern Adriatic Sea as they either move toward Koper causing stormy weather with clouds and rain, or they move southeastward causing a steep pressure gradiant over at Koper, initiating a Bora outbreak.

Bora: Bora winds result when cold air accumulates over the Balkan Peninsula, especially the region between Albania and Austria. When the depth of the cold air pool reaches the height of mountain passes, the Bora will commence.

There are two primary weather patterns associated with the Bora:

Anticyclonic pattern: A large high pressure cell is present over central Europe without a well defined low pressure center to the south.

Cyclonic pattern: A low pressure center is present in the southern Adriatic Sea or in the Ionian Sea. In either case, the pressure is higher on the European side of the mountains and lower on the Mediterranean side.

The Bora is most common in the Adriatic Sea where it flows mainly from the northeast through gaps in the Dinaric Alps. One of these gaps is near Trieste and is known as the Trieste Gap. The gap east of Koper is not as prominent as the Trieste Gap. On occasion, the Bora can be very localized, extending only a few miles offshore. At other times, the Bora will dominate the entire Adriatic Sea and, when the area of steep pressure gradiant is large enough, the Bora can extend as far south as Malta.
In the northern Adriatic Sea, the wind direction associated with the Bora is generally northeasterly but can vary in local areas due to the terrain. The Bora at Koper and Trieste is east-northeasterly. It is more northerly farther south and even northwesterly along Italy's southeast coast.

The strongest winds occur along the eastern shore of the Adriatic Sea from Trieste to the Albanian border.

Anticyclonic pattern Bora winds are most intense to the north, decreasing somewhat moving southward.

The greatest intensity of the Bora occurs where the mountain peaks are at least 2000 ft above sea level and not more than two or three miles inland.

Winds are usually less intense over the open water of the Adriatic Sea, but gale force winds (greater than or equal to 34 kt) are common. The frequency of the gale force Bora in the open sea is greater for the cyclonic type of pattern than for the anticyclonic pattern.

During the cyclonic pattern, the strongest winds are usually found in the southern Adriatic Sea.

Bora winds are most common during the cool season (November through March). In general, the frequency of gale force winds varies from one day per month, or less, in the summer to six days per month during winter months.

The average duration of a continuous gale force Bora over the Adriatic Sea is about 12 hours but the winds sometimes will last up to two days.

The average duration of a Bora that reaches gale force some time during its history is 40 hours with a maximum duration of 5 days.

At Koper, the average duration of a gale force Bora varies from three days in winter to one day in summer. Local mariners state that the Bora will last an odd number of days; 1, 3, 5, etc. However, the Bora has been known to last for up to 30 days at Trieste without a significant lull.

In 1956 a gust of 125 kt was recorded at Trieste.

The Bora does not usually start with a sudden blast but will build up at a relatively moderate pace. A 60 kt Bora will not reach peak intensity during the first 3 or 4 hours. This may allow time for some protective measures to be assessed and conducted.

Wave heights near the port of Koper are normally not high with a Bora because they are fetch limited.

There is a noticeable diurnal variation at stations along the eastern coast of the Adriatic Sea during Bora conditions. During the day, the sea breeze counteracts the offshore flow of the Bora, which decreases the strength of the Bora between 1200L and 1800L.

With the anticyclonic pattern, the Bora is basically a dry wind due to its katabatic nature. Clear skies and good visibilities are found in the lee of the mountains while thick clouds associated with up-slope motions are found on the mountain crests. These clouds subsequently dissipate in the descending air on the lee side, and appear as "cap clouds" to an observer on their west side.

With the cyclonic pattern, the Bora is often accompanied by low clouds and reduced visibilities associated with rain and/or drizzle. These conditions are more noticeable over the open water areas than along the coastal zone.
Scirocco: The Scirocco is a southeasterly to south-southwesterly wind over the Mediterranean originating over North Africa, sometimes affecting the Adriatic Sea area.
The Scirocco tends to occur year-round without a favored month or season.
The Scirocco normally occurs within the warm sector of a cyclone passing either north or west of the region. These cyclones originate either over North Africa or south of the Alps, primarily in the Gulf of Genoa in the latter case.

Scirocco conditions occur in the Gulf of Genoa case when the circulation extends far enough southward to draw air from the North African region.

The onset of the Scirocco is more gradual than the onset of a Bora. It occurs more frequently in the southern part of the Adriatic Sea with a decrease in frequency northward.

Although the Scirocco is not as strong as the Bora, winds can reach gale force (greater than or equal to 34 kt), especially in winter and spring.

The average duration of continuous gale force winds during a Scirocco is 10 to 12 hours and occasionally as long as 36 hours. The maximum wind speed likely during a Scirocco is about 55 kt. Local terrain features alter the effect of the Scirocco. Winds will parallel the coast in general.

As a cold front approaches from a relatively flat, low surface, such as the ocean, toward an elevated land mass, super-gradient winds will occur due to the Venturi effect. These winds are restricted to a narrow band between the front and the landmass and do not normally sustain for long periods of time. Seas are usually not high with strong southeasterlies due to protection from the terrain, but sustained Scirocco winds can raise seas of 6.6 to 9.8 ft (2 to 3 m) in the open water west of Koper. Waves in the harbor are fetch limited.
Genoa Lows: Genoa lows are low-pressure systems which develop to the south of the Alps in the region incorporating the Gulf of Genoa, Ligurian Sea, Po Valley, Gulf of Venice and northern Adriatic Sea. Although several factors are important in cyclogenesis, the development of the cyclone near the Gulf of Venice--as opposed to the west near the Gulf of Genoa--depends on the amount of cold air penetrating the Po Valley from the northeast. If there is little or no cold air entering the Po Valley, the low will probably form in the Gulf of Venice; otherwise, cyclogenesis will occur to the west. Genoa cyclones usually remain stationary (or at least leave a residual trough) south of the Alps throughout their life history. If the lows do move, they generally follow one of two tracks.
The first track, common for cyclones developing in the Gulf of Venice, is a northeasterly to north-northeasterly direction across the Alps. This track is associated with strong southwesterly flow aloft. In this case, Scirocco conditions are likely if the circulation of the low extends southward into North Africa, allowing air from the desert source to move northward.
The second track, associated with a strong anticyclone over the Balkans, Turkey and the Black Sea, is in a southeasterly direction from the Gulf of Genoa towards the Ionian Sea. In this case, a gale force Bora is extremely likely by the time the depression moves into the Ionian Sea.

Heat Index and Windchill Charts

Source:

Naval Research Laboratory Marine Meteorology Division - https://www.nrlmry.navy.mil/~cannon/medports/Koper/index.html

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