CHIEF OF NAVAL OPERATIONS
15 August 1943
18 January 1944
This is one of a series of pamphlets dealing with the weather aspects of Naval and Amphibious Warfare. The data on which these studies are based are taken from official documents and reports submitted to the Navy Department. The material has been collated and presented in a semi-technical form with particular attention given to the operational aspects of weather.
During the preparation of this study, it was found that weather data submitted by the various commands were occasionally at variance. An effort has been made to reconcile these differences in order to provide an accurate account of the sequence of weather conditions as forecast for the Force Commander, to describe the actual weather conditions observed during the operation, and to give a practical explanation of these weather conditions.
It is hoped that these studies will afford a clear view of the use of weather information during the planning, strategical, and tactical phases of the operation, and that they will form a basis for a hotter understanding of the application of weather information in future operations.
The primary objective of these analyses is to assist those officers who are charged with the responsibility for the planning and execution of similar operations.
Vice Admiral, U.S.N.,
Deputy Chief of Naval Operations, (Air).
TOPOGRAPHICAL MAP OF KISKA
The Occupation of Kiska
Weather in the Aleutians
An operation scheduled in the Aleutian Island area is most dependent on weather. These islands, located far out in the Pacific and at the point of interaction of the cold ocean currents to the north and the warmer ones from the south, are subject to more bad weather than almost any other region of the world. In an attempt to simplify a very complex situation, it may be said that the predominance of bad weather during the summer season can be attributed to two main factors. Normally, during this season, there is a region of high pressure fairly stationary off the west coast of the American continent. Weather fronts which originate in Asia proceed across the Pacific and become stalled against the western portion of this region of high pressure. Along a stationary front, open waves (small storm centers) often develop with great frequency and travel at high speed along the front. These waves, traveling northeastward along the western boundary of the high pressure area, pass the Aleutian Island chain, bringing with them periods of bad weather.
The second factor producing bad weather conditions in this region is the almost daily appearance of fog over some part of the Aleutian chain. The air, traveling from the south over the warm waters of the Pacific, acquires a relatively high moisture content. When the air finally comes over the cool waters immediately south of the islands, rapid cooling results in the condensation of the excess moisture and fog rolls up on the southern shores. Frequently, the layer of fog is so shallow that it does not pour over the mountainous ridge which forms the spine of the chain. During this shallow fog condition, the leeward portions of the mountainous islands often remain clear. If the fog does become deep enough to cover the mountains, the downward motion of the air on the lee side causes a warming which is often sufficient to dissipate the fog.
Flying, around these islands, is severely restricted in that fog may obscure the air bases or the target. The dissipating effect on the lee side of the mountains and diurnal heating of the land masses result in the lifting or breaking of the fog. This phenomenon can, however, be predicted so that more air operation is actually possible than would be indicated superficially.
Air Operations from Aleutian Airfields
Prior to our occupation of Kiska, bombing and strafing missions were sent out from our bases on Adak, Amchitka, and Attu in an attempt to make the Japanese position in the Aleutians untenable. In spite of the fact that unfavorable terminal or frontal conditions alone prevented the activity of our planes, during July 1943 only 12 days of aerial bombardment were possible. During August, these missions were practicable on only 10 days. Of the three bases, Adak was the most satisfactory since even with widespread fog conditions, the airfield on this island usually remained open. At Adak, the field is situated on the north side of the island, protected from the south, east, and west by mountains. The fog was usually found banked up to the south and west of the island. When the fog became deep enough to windward to pour over
the mountain tops, a ceiling of about one thousand feet was usually maintained, which was often burned off over the field by the diurnal heating effect. Only sea breezes or winds from the north and northeast, both of which were unusual, served to close the field.
Amchitka, a relatively low and flat island, was found to be most unsatisfactory for summer operation since it was closed about fifty percent of the time.
Attu, while suffering from the same difficulty of having a flying field which was frequently closed, was well adapted for amphibious Catalina operations. When conditions on the southeast side of the island became unfavorable, it was usually possible to make water landings at Holtz Bay on the north side.
The bombing missions were completed either by ordinary visual bombing when visibility over the target was adequate or by time-distance bombing using the Kiska volcano as the point of departure. This convenient landmark was usually clear of the top of the overcast.
In addition to these missions, scouting planes were sent out to search the adjacent waters and several diversionary raids were made against Paramushiro. Seven of these flights were made. To illustrate the difficulties of air operations in this region, the following table lists the results of these missions.
Date Result 10 July Overcast over target area. Top at 7,000 8,000 feet. Bombed on time-distance run from landmark on Kamchatka. 10-11 July (night) Turned back 20 miles from target due to solid overcast extending to 12,000 feet. 11 July (day) Solid overcast -- turned back. 18 July (day) Scattered clouds -- successful attack. 18-19 July (night) High and middle overcast over target -- turned back. 11 August (day) Clear -- successful attack.
In addition to the air operations during July and August, the Navy maintained strong battleship and cruiser task groups blockading the western approaches to Kiska. A closer blockade of this island was maintained by two destroyers which also shelled enemy installations at irregular intervals -- on eleven nights in July and on seven nights in August.
With respect to surface operations, as well, the prevalent fog played an important role. On an average of once every five days, the task groups rendezvoused with tankers and refueled at sea. Fog and low visibility conditions were almost invariably encountered, but despite this, all rendezvous were
Preliminary Surface Operations
successfully effected. Although the fog acted only as an inconvenience in this aspect of surface operations, the effectiveness of these task forces in imposing a total blockade of the Japanese on Kiska was seriously diminished. Enemy ships were able to pass through our blockade under cover of fog.
Weather Requirements for Surface Bombardment
For the small-scale bombardment of Kiska by our surface forces, fog was considered advantageous as it offered a measure of protection against enemy gunfire. For these large-scale bombardments, involving many vessels and large areas, it was desirable to have weather conditions which permitted the use of visual fire control.
On the four occasions when major bombardment was carried out, a careful study of present and forecast weather conditions was made in an effort to insure the maximum weather advantage to our forces. The synoptic situation desired was one involving westerly winds, a few middle or high clouds, and patchy fog. These conditions could be forecast one or two days in advance and the operation scheduled to coincide with the favorable situation.
In an effort to keep a constant check on weather conditions, the following procedure was adopted for the period prior to Baker Hour:
1. Two or three weather planes took station three hours prior to Baker Hour: one covering the target and firing area to the northeast of Kiska harbor, if firing was to be conducted in that area; one covering the target and firing area to the south and southeast from Sobaka Rock to Little Kiska Island; and one, thirty to forty miles upwind from Kiska. These planes made hourly weather reports to the Task Force Commander which were intercepted by the Firing Groups. Particular emphasis was placed upon reporting wind, ceiling, visibility, and fog conditions.
2. At Baker minus four to Baker minus three hours, the blockading destroyers commenced transmitting hourly weather reports in the firing and target areas, with detailed descriptions of fog conditions. These reports were also intercepted by the Firing Groups.
3. At Baker hour, the firing group or groups prepared to commence high-speed runs to the firing areas. With the information at hand, the officer in tactical command was in a position to determine whether satisfactory conditions would maintain or develop. He had complete discretion to delay the approach or to postpone the bombardment. When the approach was started, he so reported and the second firing group was able to coordinate its approach. Weather reports were continued until one hour prior to commencement of firing when destroyers cleared the area and weather planes took stations for spotting.
In three of the four cases, bombardment was scheduled for about 1400 to 1500 local time to obtain the maximum visibility and ceiling resulting from diurnal heating. The fourth bombardment was carried out during the early morning, on one of the few occasions when the weather forecast indicated that favorable conditions would prevail at that time.
The above procedure was generally successful. Satisfactory visibility obtained at all times except during the bombardment of 6 July when fog and low clouds partially obscured the target area toward the end of the firing run.
An area of high pressure extending over the Aleutian Island chain produces southeasterly winds over Kiska. This synoptic situation on 15 August 1943 permitted our forces to make a landing on the lee side of the island.
The more usual situation consists of a low pressure area extending over some portion of the Aleutian Islands. With this weather pattern the wester part of the island chain has northwesterly winds. The landing at Kiska would have been difficult had this weather situation prevailed on 15 August.
The Occupation of Kiska
Weather requirements for landing on Kiska
These surface and air operations were merely preliminary to the occupation of Kiska Island. Although considerations other than weather dictated the time for the final attack, it was realized that the period chosen for the operation would probably be one of fog, low ceiling, and visibility and that air support could not be counted upon. Basic plans did, however, include full air support, including observation, spotting, strafing, and bombing in the eventuality that weather conditions would permit air activity.
The weather most desirable for the landing operation is listed below:
1. Favorable winds and seas during the passage of convoys from Adak and Amchitka to Kiska were required for the safety of landing craft. In addition it was desired that troops be kept embarked for as short a time as possible.
2. In the beach and transport areas on the northwest side of the island, desirable landing conditions included favorable surf conditions and winds not greater than 15-18 knots. A wind direction from southwest through west to north was most undesirable. The preferred direction was the sector between south and east. With a wind from this direction, the beaches selected would be in the lee of the island.
3. For navigational purposes, a minimum of 2-3 mile visibility and 500-1,000 foot ceiling was required for the landings.
Forecasting for the Kiska landing operation
To assist in the planning of the operation, the 1200 GCT weather map was analyzed in detail during each morning. Prior to noon a daily weather conference was held, attended by aerologists from each of the units taking part in the final operation. From information at hand, agreement was reached upon the synoptic situation and forecasts to be issued. Prior to the presentation of the analysis and forecasts, the analysis was projected forward to 1800 GCT and modified as necessary by available 1800 GCT reports from the Aleutians and by early reports from search planes. The results of this aerological conference were made available each day at 1330.
To illustrate the type of weather information which might be supplied during the planning stages of an operation and to show how the pattern of air masses existing over the islands around 15 August differed from the mean, a typical August map for the Aleutian area has been reproduced herewith (p.6-7). In the selection of this map, a file of 10 years of August maps was studied before that for 28 August, 1932, was chosen. The centers of pressure systems in the vicinity of the Aleutians were plotted for the ten-year period. With the positions determined from the plot, a synoptic map with high and low pressure areas located in the mean positions was selected from the file. There were a number of maps which could have been chosen. The one for 28 August, 1932, was one of the simplest.
In contrast to the weather pattern appearing on this typical map, the synoptic map for 15 August shows a high pressure area extending over the entire
TYPICAL NO. PACIFIC MAP FOR MONTH OF AUGUST
WEATHER MAP FOR 0130 10 AUGUST 1943
WEATHER MAP FOR 0130 11 AUGUST 1943
WEATHER MAP FOR 0130 12 AUGUST 1943
WEATHER MAP FOR 0130 13 AUGUST 1943
WEATHER MAP FOR 0130 14 AUGUST 1943
chain of islands. With the persistent high so situated, no wave development along the cold front could push its way across the island chain. Thus, the winds would not shift from their southeasterly direction into northwesterly.
In planning the operation, it was vital to know at the earliest possible time whether there was any likelihood of the high pressure area breaking down or moving eastward.
Auxiliary Weather Information
Operations could continue with maximum efficiency only as long as favorable weather conditions prevailed. Since the first sign of an unfavorable development would be a decrease in atmospheric pressure to the west of the island chain, a submarine was dispatched to a station about 600 miles southwest of Kiska in the vicinity of latitude 47°N and longitude 165°E. Weather reports were transmitted at six-hourly intervals while enroute to, and while on station. An aerographer's mate was assigned to the submarine for the purpose of taking these observations. Throughout the period during which the submarine broadcast weather data, the indications were that the high pressure area was moving very slowly eastward from its position over the Aleutian Islands. The motion was too slow, however, to indicate that any radical change in the weather would develop and did not cause particular concern.
Weather 10-15 August
The synoptic situation for the period between 10 and 15 August showed relatively stable and well-developed tropical maritime air covering the north-central and northeast Pacific. A strong polar continental air mass, transformed slowly into polar maritime, was feeding into the Sea of Okhotsk and southwest of the Kamchatka peninsula. A frontal system extended southwest of Umnak Island. As the polar mass became warmer and stronger, its center moved eastward south of the western Aleutians. From 11 to 14 August, the two highs merged. Throughout this period, a series of weather disturbances moved northeast along the China coast and Kuriles building up on Kamchatka. However, as long as the high to the eastward maintained, these disturbances were blocked.
On 13 August, the Task Force Commander issued the following forecast for the 15th:
"Kiska -- 15 August: Low overcast with extensive fog areas. Wind south to southeast ten to fifteen knots."
The following day, the forecast was expanded to:
"Kiska and surrounding sea area, 15 August: Overcast sky with fog and drizzle; ceiling and visibility near zero throughout open sea areas and on southeast (windward) side of Kiska. On northwest side of island, slight clearing of fog with base of low overcast at 500 to 1,000 feet, tops at 2,000 -3,000 feet; visibility 3-5 miles; scattered high clouds. in open sea, winds south to southeast 15-20 knots. No appreciable change in Kiska weather expected through Dog plus One Day."
WEATHER MAP FOR 0130 15 AUGUST 1943
The first report concerning weather conditions on the 15th indicated that the forecast had been verified. Later reports from the lee side of the island in the vicinity of the landing beaches gave weather as follows: "Overcast, fog, visibility 3-5 miles, ceiling 500-1,000 feet, wind southeast 10 knots. Surf conditions favorable to boating."
Only on the 15th were there any positive indications that a frontal system was approaching from the west. Reference to the map for 16 August on page 16 shows the position of this front. Although the wind direction at Kiska would change with the frontal passage, by this time the initial landings would be completed and the wind direction would no longer be a matter of major importance.
Operations around the Aleutian Islands at this time demonstrated a number of highly important precepts concerning the strategic and tactical use of weather.
1. The recognition of favorable weather conditions contributed to the speed and efficiency of the occupation of Kiska. Although a study of average weather conditions indicated that these might not be entirely favorable, a detailed analysis of day-to-day weather maps made possible close coordination between scheduled operations and weather.
Experience to date gives adequate support to the conclusion that, in the final stages, the weather requirements of an operation are a specific forecasting problem which cannot be solved entirely by reliance upon average weather conditions.
It is not intended to imply here that a statistical study of average weather conditions is without meaning. On the contrary, the most satisfactory employment of weather in the planning of an operation is directly related to such a consideration. It would he desirable to schedule all operations so that they coincide with the period which, on the basis of Climatological evidence, is most favorable.
It is realized, however, that more often than not, operations are scheduled on the basis of strategic and tactical considerations which outweigh the weather factor involved. The determination of expected weather conditions by the examination of averages is, then, still important in that it enables the planners to take account of those tactical and logistic elements which are related directly to average conditions. The choice of landing beaches, the location of airstrips, the selection of the proper types of clothing and shelter are a few of the considerations to which average weather is important.
2. Throughout the entire period, the planning of operations incident to the landing at Kiska had to take account of fog conditions. It had been decided to harass and attack the enemy at every opportunity prior to the actual landing. Had it been impossible to forecast periods of time during which good visibility
WEATHER MAP FOR 0130 16 AUGUST 1943
would prevail, the number of opportunities would have been few. As it was, the attack groups could be informed on occasion that "the fog now over the target will lift by XXXX hour" and forces could plan their missions accordingly. The careful study of local topographical effects together with a knowledge of the principles of fog forecasting proved invaluable.
3. During the preliminary bombardment of enemy bases by aircraft, weather over the target was not the only limitation imposed upon air activity. Of equal importance were weather conditions at the home base. In this connection, it should again be pointed out that air operations were often possible on the north end of Attu although at the same time the field on the south side of the same island was closed due to fog. The effect of topographic features upon local weather conditions will continue to be a major consideration in the selection of sites for airfields to be used in future operations.
4. Most significant of all was the use of auxiliary weather aids in connection with the occupation of Kiska. For both the preliminary bombardment and the landings, a definite weather pattern was required if the operations were to proceed with maximum speed and minimum loss. In order to overcome the handicap to accurate weather analysis caused by the existence of large gaps in the reporting network of stations, planes, destroyers, and submarines were employed as temporary observing stations.
This excellent use of available tools in overcoming an inherently difficult situation during the occupation of Kiska is outstanding. The use of auxiliary weather observers in future operations may prove equally valuable.