WIND ATLAS OF THE NORTH PACIFIC ,.,, Biological UboraioTjl MAR 2 01958 VWWDS HOLE, MASS. SPECIAL SCIENTIFIC REPORT- FISHERIES No. 243 UNITED STATES DEPARTMENT OF THE INTERIOR FISH AND WILDLIFE SERVICE Explanatory Note The series embodies results of investigations, usually of restricted scope, intended to aid or direct management or utilization practices and as guides for administrative or legislative action. It is issued in limited quantities for the official use of Federal, State or cooperating Agencies and in processed form for economy and to avoid delay in publication. United States Department of the Interior, Fred A. Seaton, Secretary Fish and Wildlife Service, Arnie J. Suomela, Comtnissioner WIND ATLAS OF THE NORTH PACIFIC By James W. McGary, Oceanographer and Thomas M. Naito, Fishery Aid Pacific Oceanic Fishery Investigations Honolulu, T. H. Special Scientific Report--Fisheries No. 243 WASHINGTON: September 1957 ABSTRACT This atlas comprises a summary of average wind speeds in the Pacific north of 30*N. latitude, and was prepared with the hope that it would aid the fishing industry in evaluating fishing conditions and potentialities in that region. The data were obtained from the current files of unpublished wind data nnaintained by the U. S. Weather Bureau. They represent observations made over a 60-year period by a great number of ships traversing the area. For each month, with a few exceptions, there are 5 charts; the first 4 indicate the geographical variations of the observed wind speeds that were < 20, < 25, < 30, and < 35 knots respectively. The fifth chart gives the maximum observed wind in Beaufort scale for each 5-degree square of latitude and longitude. CONTENTS Page Source of data 3 Reliability of the data 3 Procedures 5 Use of the charts in evaluating operational potentialities in various areas 6 Acknowledgments 7 Literature cited 7 Chart index 8 Charts 1-53 9-35 FRONTISPIECE Hauling gill nets in a 30-knot wind in the North Pacific on Cruise 33 of the John R. Manning. WIND ATLAS OF THE NORTH PACIFIC By James W. McGary, Oceanographer and Thomas M. Naito, Fishery Aid Pacific Oceanic Fishery Investigations Honolulu, T. H. In commercial fishing, as in any other maritime operation, weather must be consi- dered when evaluating the operating potentiali- ties of an area. Regardless of the abundance of fish, if wind and sea prevent a vessel from obtaining pay loads, the area has greatly re- duced value for a commercial fishery. The results of the first three exploratory fishing cruises of vessels of the Pacific Oceanic Fish- ery Investigations {POFI)to the waters north of Hawaii in search of new albacore grounds denn- onstrated this situation quite strikingly. On IZ of the 25 days spent north of 30*N. latitude, on John R. Manning cruise 19 (January- March 1954), the seas were considered too rough for longlining. On John R. Manning cruise 22 (September-November 1954), on 18 of 41 days, sea conditions were not suitable for fishing, and onJohnR. Manning cruise 23 (January-February 1955), fishing was not possible on 9 of 25 days (Shomura and Otsu 1956). Furthermore, the northern limit of the albacore distribution in the central North Pacific during the fall and winter months could not be definitely established because adverse weather forced the vessels to turn south. As the result of this experience, work was started on a guide which, it was hoped, would aid in evaluating the operational limitations of small (80 to 130 feet) vessels at different sea- sons of the year in the North Pacific above 30 *N. latitude. The resulting atlas consists of a series of four contour charts for each month, (with a few exceptions) showing the frequency of winds of 20 knots or less, 25 knots or less, 30 knots or less, and 35 knots or less, and a fifth show- ing the maximum wind that has been observed in each 5-degree square of latitude and longi- tude (charts 1-53). The existing wind summaries (e.g., McDonald 1938, U. S. Navy 1956) publishedfor the benefit of mariners in the North Pacific pro- vide a wealth of data on average winds, percent- age of winds of gale force or greater, and per- centage of calms. While these data are useful they do not provide the essential information for evaluating operating areas in terms of potential operating time for fishing vessels since they do not provide a precise breakdown of data in the 20-30 knot range, where experience has shown that most fishing operations must cease. Ideally, sea height would be a better indi- cator of operating conditions than wind, but there is not a sufficient nunnber of wave observations available for the North Pacific to permit the prep- aration of reliable charts. The U. S. Weather Bureau and the U. S. Navy Hydrographic Office have been compiling wind data from ships' weather reports and deck logs since the latter part of the 19thcentury, but it was only recently, September 1, 1955, that a concerted effort was made to have all vessels report sea conditions (A. J. Rohlfs, USWB personal connmunication). The relation between wind and sea has long been recognized, and sea characteristics are still used as the basis for estinnating wind speed on vessels not equipped with anemometers (Bowditch 1953, p, 52). The validity of using wind as an indicator of sea state has also been demonstrated in the development of wave-forecasting techniques. Sverdrup and Munk (194 7) derived equations for computing wave height and velocity from wind velocity, duration of wind, and fetch. Duration of wind refers to the period of time during which the wind velocity has been approximately uni- form. Fetch is the length of the generating area or the distance over which the wind velocity has been approximately steady. Detailed instruc - tions for connputing these parameter s and wave- forecasting techniques are given in USNHO Miscellaneous Publication 11275. Sverdrup and Munk (1947, p. 31) also found that the British Admiralty's empirical rule that waves lose roughly one -third of their height each tinne they travel a distance in miles equal to their length in feet was in general agreement with theoreti - cal values and could be used to estimate the decay rate of waves after they left the genera- ting area. From data in Wave Report No. 73 (unpub- lished), Scripps Institution of Oceanography , table 1 was compiled showing the minimum time Table 1. --Minimum time and fetch required for winds of various velocities to produce waves of a given height and the length of the waves produced under these conditions. (Calculated from Wave Report No. 73 (unpublished) of Scripps Institution of Oceanography, University of California) To produce waves -- At a wind velocity of -- 20 25 30 35 40 45 50 55 60 knots knots knots knots knots knots knots knots knots 4 feet high: Time (hours) 3.2 2.0 1. 3 1.0 0.9 0.8 0.7 0. 6 0.5 Fetch (nautical miles) 11 7 < 5 < 5 < 5 < 5 < 5 < 5 < 5 Length (feet) 40 43 46 49 50 51 51 52 52 8 feet high: Time 19.0 6.2 4. 0 3.0 2.2 1.9 1. 5 1.2 1.0 Fetch 120 26 18 14 11 9 7 6 5 Length 155 86 82 86 86 90 95 95 95 12 feet high: Time 20.0 8.0 5.4 4.0 3. 1 2.8 2.2 2.0 Fetch 74 5 48 31 22 17 17 13 12 Length 216 133 123 125 133 138 138 141 16 feet high: Time 16.2 8.9 6. 3 4.9 3.9 3. 1 2.9 Fetch 125 59 42 32 26 20 19 Length 237 172 166 166 172 178 178 20 feet high: Time 14.0 9. 1 7.0 5. 7 4.8 4.0 Fetch 120 67 51 42 36 29 Length 258 216 206 207 210 213 24 feet high: Time 31.0 13.4 9.5 7. 3 6.0 5. 1 Fetch 320 115 76 59 48 41 Length 462 288 258 244 237 251 28 feet high: Time 20.9 13.0 9.7 7.8 6.4 Fetch 210 120 84 68 56 Length 406 328 296 288 280 32 feet high: Time 36.5 16.7 12.0 9.4 7.8 Fetch 440 170 115 87 71 Length 620 401 344 324 320 36 feet high: Time 24.4 15.4 11.6 9.3 Fetch 280 160 120 91 Length 533 424 379 361 40 feet high: Time 42.0 19.5 14.2 11.4 Fetch 575 220 150 120 Length 787 512 44 3 415 44 feet high: Time 25.6 16.0 13.4 Fetch 315 180 150 Length 642 512 462 Table 1. --Minimum time and fetch required for winds of various velocities to produce waves of a given height and the length of the waves produced under these conditions. (Calculated from Wave Report No. 73 (unpublished) of Scripps Institution of Oceanography, University of California) (cont'd) To produce waves -- At a wind velocity of -- 20 25 30 35 40 45 50 55 60 knots knots knots knots knots knots knots knots knots 48 feet high: Time (hours) 43.0 21.2 16.3 Fetch (nautical miles) 635 265 190 Length (feet) 919 608 54 3 52 feet high: Time 25.8 18. 1 Fetch 340 220 Length 713 608 56 feet high: Time 36. 1 21.5 Fetch 535 280 Length 919 677 60 feet high: 52.5 26,0 Time 890 355 Fetch 1214 800 Length and fetch required for winds of 20 to 60 knots to generate waves of various heights. These data are useful for estimating the maximum waves to be expected from storms at sea. The wave length was also included in the table to aid in estimating the wave heights to be expected downwind from storm areas. Wave length was computed from the periods given in the graphs by the formula L = 5. 12t2 where L is the length in feet and T is the period in seconds (USNHO 1944). SOURCE OF DATA The data used in constructing the wind frequency charts were supplied by the U. S. Weather Bureau Records Center, Asheville, N. C. , from their current files of unpublished marine wind tabulations as of May 1955. The data consist of tabulated individual Beaufort force frequencies for each month for each 5- degree square of latitude and longitude in the North Pacific and adjacent seas north of 30 'N. latitude. The observations cover a period of more than 60 years. The total number of ob- servations per square varies greatly. The squares in the regular steamer lanes have as many as 5, 808 observations for a single month. but many areas in the extreme northern portion have no reports during the winter months. RELIABILITY OF THE DATA Even at the present time only about 50 per- cent of the vessels plying the North Pacific are equipped with an anemometer (A. J. Rohlfs, USWB, personal communication) so most of the wind speeds have been reported in Beaufort scale estimates. For convenience in keeping records, the speeds observed by vessels having anemometers were also converted to the Beau- fort scale. In the original scale, devised about 1805 by Admiral Beaufort of the British Navy, the effects of wind on a ship's sails were used as criteria for estimating the wind force (Byers 1944, p. 83). Since that time the criteria for estimating Beaufort force have been adapted to fit a variety of circumstances (Riesenberg 1936, p. 794; Bowditch 1943, p. 52), and the wind speed in knots corresponding to the various forces have been determined experimentally . On steam vessels the state of the sea has been connmonly used for estimating wind speed. The criteria for this method, approved by the Inter- national Maritime Conference and in current use, are given in table 2 together with the range in knots and descriptive term for each force (USWB 1954, p. 14). Obviously such subjective Table 2. --Determination of wind speed by sea condition (from USWB Circular M, 1954. p. 14) Wind force (Beaufort) Speed in knots Descriptive terms Sea conditions 10 11 12 Less than 1 1-3 4-6 7-10 11-16 17-21 22-27 28-33 34-40 41-47 48-55 56-63 64 and above Calm Light air Light breeze Gentle breeze Moderate breeze Fresh breeze Strong breeze Moderate gale Fresh gale Strong gale Whole gale Stornn Hurricane Sea smooth and mirror-like Scale-like ripples without foam crests Small, short wavelets; crests have a glassy appearance and do not break. Large wavelets; some crests begin to break; foan-i of glassy appearance. Occasional white foam crests. Small waves, becoming longer; far-rly frequent white foam crests. Moderate waves, taking a nnore pronounced long form; many white foam crests; there may be some spray. Large waves begin to form; white foam crests are more extensive everywhere; there may be some spray. Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind; spindrift begins. Moderately high waves of greater length; edges of crests break into spindrift; foam is blown in well-marked streaks along the direction of the wind. High waves; dense streaks of foam along the direction of the wind; crests of waves begin to topple, tumble, and roll over; spray nnay reduce visibility. Very high waves with long overhanging crests. The resulting foam in great patches is blown in dense white streaks along the direction of the wind. On the whole, the surface of the sea is white in appearance. The tumbling of the sea becomes heavy and shocklike. Visi- bility is reduced. Exceptionally high waves that may obscure small and medium-sized ships. The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility reduced. The air is filled with foam and spray. Sea completely white with driving spray; visi- bility very much reduced. methods of estimating wind speeds must have resulted in considerable differences among individual observers. Excellent results have been obtained, however, in oceanographic com- putations using ships' wind data by assuming that the observed values for a given Beaufort force form a Gaussian distribution about its midpoint and have a standard deviation of half a Beaufort interval {Reid 1948). Apart from estimating the reliability of single observations on wind force is the prob- lenn of setting the mininnum number of obser- vations needed to give a reliable estinnate of the wind forces over a given 5-degree square of ocean during a given month; that is, assum- ing observations are randomly distributed in time, how many are needed to furnish a reliable description of the winds in a 5-degree block of ocean during one nnonth? Since the estimated standard deviation of a single observation is one-half a Beaufort force class, it was arbi- trarily decided that the data from a 5-degree square for a particular month would not be considered unless there were enough observa - tions to furnish a mean having a high probabil- ity of lying within 0. 5 of a Beaufort force of the true mean. Following Snedecor (1946, p. 457) this minimum sample size was estimated by computing the standard deviation and standard error of the mean of a square from midocean represented by 427 observations. From these statistics n was computed for the 99-percent and 95-percent confidence levels as 37 and 27 respectively. In constructing the monthly charts all squares having less than 27 observa- tions were omitted and the contours of the areas having between 27 and 37 observations were drawn with dotted lines. PROCEDURES Since marine weather reports and fore- casts are now made in knots rather than in Beaufort scale, knots were used in the charts in this atlas, which show for each nnonth the percentage of observed winds of 20, 25, 30, and 35 knots or less. Twenty knots was selected as the lowest speed for contouring, since at this wind speed any seagoing fishing vessel should still be able to carry out all types of fishing operations. It is slightly greater than the mid- point of Beaufort force 7 (17-21 knots) which is defined as the speed at which "smacks shorten sail" (Bowditch 194 3, p. 52) and at which the U. S. Coast Guard begins to display small-craft warnings. Thirty-five knots was selected as the maxinnum wind speed for fishing operations because it lies in the lower limits of Beaufort force 8 (34-40 knots), which is defined as the speed at which "smacks remain in harbor, and those at sea lie to." The two intermediate velocities have been included as a basis for estimating the percentage of time larger ves- sels should be able to carry out limited opera- tions such as trolling, or that smaller vessels must "lie to, " The experience of POFI vessels in the North Pacific has shown the validity of these limits. At wind speeds of 20 knots, gill nets begin to tangle and are difficult to retrieve, and longlining becomes extremely difficult. The records show that longline has been laid in winds up to 25 knots but only when the 30-hour weather forecast indicated that the weather would moderate, and there were other signs of improving weather. Both gill nets and longline s have been retrieved in winds up to 35 knots when it was a matter of saving the gear, but the operation was exceedingly difficult and hazard- ous. Thirty knots represents the upper limit of trolling; above this speed the lines tangle and do not fish properly. It has been POFI's expe- rience that, above 35 knots, her research ves- sels must suspend fishing activities and either lie to or jog into or before the sea, depending on their particular characteristics. The percentages used in preparing the con- tour charts were obtained from cumulative per- centage distribution curves of the wind speeds . Monthly cunnulative distribution curves for each square were constructed by first plotting the cumulative percentages for each Beaufort force at the speed in knots equivalent to the extreme upper limit; e.g., 16.5 knots for force 4. These points were then used as a basis for drawing smoothed ogive curves (Guilford 1950, pp. 121- 126). Actually the smoothed curves passed through the points in the majority of cases. The percentiles for the 20-, 25-, 30-, and 35-knot levels were then taken fronn these curves. The percentages were plotted at the mid- point of each square and the contours were drawn assuming that they represented the fre- quency at this point. After the values were plotted, examination showed that some of the squares off North America and Japan, which were largely land, e.g., the square bounded by 50°-55°N., 125'-130°W., and the confined waters between Japan and Asia had a much larger percentage of winds of lower speeds than the adjacent areas offshore. It was believed that this apparent increase in percentage of winds of lower speeds was due to vessels taking advantage of shelter when operating locally or awaiting good weather before departing from port. Data for these squares were therefore omitted from the chart. Another area where, in winter, the percentage of low-speed winds also seems abnormally higher than climatolog- ical data would indicate i s the band between 50° and 55 'N. latitude. The primary storm track, i. e. , the path of the maximum concen- tration of individual storm tracks, lies in this band between October and April (U. S. Navy 1956), and hence the minimum percentage fre- quency of low winds would be expected. Such an abnornnality in the records may have resulted from vessels taking shelter in the Aleutian Islands during periods of high winds . This tendency of wind data to become skewed towards lower speeds in coastal and insular areas will tend to become oceanwide in the future as more and more vessels tzike advan- tage of the increasing reliability and dissemi - nation of marine weather forecasts in choosing their sailing routes. The plots of maximum wind simply show the maximum Beaufort force that has been reported in each unit of area, regardless of the number of observations. Forces of 8 or less have been lumped into a single group, since lower speeds are adequately covered in the contour charts. In the majority of the squares the mJLximum values comprise less than 1 per- cent of the total observations, and in a large number of the areas they represent single observations. Nevertheless, they indicate wrind speeds that have occurred and speeds that a vessel should be able to withstand if it is to operate in the area. USE OF THE CHAKTS IN EVALUATING OPERATIONAL POTENTIALITIES IN VARIOUS AREAS The most practical method of illustrating the use of the charts is to compare the actual conditions encountered by POFI vessels with the average conditions indicated by the charts. Taking the most adverse season first, during John R. Manning cruise 19, some excellent longline catches of albacore were made in late January 1954 along 160'W. between 30* and 35 'N. latitude, but because of rough seas, fish- ing was possible on only 4 of 7 days, or 57 per- cent of the time. The weather log shows that cnly 15 (65 percent) of the 23 wind observations were 20 knots or less and winds up to 50 knots were reported. Charts 1-5 show that the per- centage of winds of 20 knots or less which might be expected in January lies between 60 and 65 percent and that the maximunn speed is Beaufort force 1 1 or 56-63 knots. Thus it appears that the charts of winds of 20 knots or less give a fair estimate, although slightly on the high side in this case, of the percentage of time the Manning could expect to longline in the area. Considering next the summer season, when the best conditions occur, and again using the John R. Manning as the example, on cruise 32 of the Manning (July 25 to Septennber 3, 1956) excellent gill-net and troll catches of albacore were made in the area from 145*W. to 175*W. longitude, between 42*N. and48*N. latitude (POFI unpublished data). During the cruise two independent series of wind observations were made, one by the scientists as part of the stand- ard 6-hour weather observations and the other by the ship's officers at the end of each 4-hour watch. The officers also logged additional observations during periods of high winds. Both series indicated that the wind frequencies were about what the August charts (charts 32-34), the midpoint of the cruise period, indicate for the area. Of the 121 observations nnade by the scientists 90 percent were 20 knots or less, 96 percent were 25knots or less, and the maximum was 30 knots. Of the 127 reports by the ship's officers, including the special observations, 87 percent were 20 knots or less, 94 percent 25 knots or less, 99 percent 30 knots or less, and the maxinnum was 32 knots. The observed con- ditions lie within the 85-90 percent range of the frequency of winds of 20 knots or less indicated for the area by the August chart (chart 32). During this cruise the weather conditions per- mitted gill nets to be set at 23 of the 26 planned stations, or 88 percent of the time. Thus, the frequency of winds of 20 knots or less appears to be an excellent index of t h e percentage of time suitable for gill netting. The trolling log showed that conditions were suitable for trolling with all lines (6) on 28-1/2 days and with a reduced number of lines on 2 days, for a total of 92 percent of the 32 days actually spent in the area. Although trolling was performed in winds of up to 27 knots under exceptional sea condi- tions, a comparison of the observed wind fre- quencies and the total trolling time indicates a more reliable index of the probable trolling time for the Manning would be about midway between tlie frequencies of winds of 20 and 25 knots or less. The actual working limit of each vessel must be determined in the above manner by ex- perience. Once this has been established, a reliable estimate of the time that it could expect to fish in the North Pacific can be obtained from the charts. It is apparent, however, from the frequency with which forces 10-12 appear in the charts of maximum observed wind for the sum- nner months, that a vessel must be capable of riding out the seas generated by such winds if it is to operate in the open North Pacific during any season of the year. ACKNOWLEDGMENTS The authors wish to express their appre- ciation to the many persons who contributed to this atlas. The data represent the efforts of many thousands of ships' officers and quarter- ma s t e r s . The data were located and made available by Roy L. Fox of the U. S. Weather Bureau. Dorothy D. Stewart made the statis- tical computations, Richard Callaway made the wave calculations, and Tamotsu Nakata drafted the charts. relations for forecasting. U. S. Navy Hydrographic Office Pub. No. 601. 44 p. U. S. NAVY, CHIEF OF NAVAL OPERATIONS 1956. U. S. Navy marine climatic atlas of the world. Volunne II. North Pacific Ocean. U. S. Governnnent Printing Office, Washington. 275 p. U. S. NAVY HYDROGRAPHIC OFFICE 1944. Wind waves and swell: Principles in forecasting. Hydrographic Office Miscellaneous publication 11275. 69 p. LITERATURE CITED BOWDTICH, N. 1943. American practical navigator. U. S. Government Printing Office, Washington. 387 p. BYERS, H. R. 1944. General meteorology. McGraw-Hill Book Co. , New York. 645 p. GUILFORD, J. P. 1950. Fundamental statistics inpsychology and education. McGraw-Hill Book Co. , New York. 633 p. McDonald, w. f. 1938. Atlas of climatic charts of the ocean. U. S, Weather Bureau No. 1247, 65 p. RELD, R, O. 1948. The equatorial currents of the eastern Pacific as maintained by the stress of the wind. Jour. Mar. Res. 7(2): 74-99. RIESENBERG, F. 1936. Standard seamanship for the Merchant Service. Van Nostrand Co. , New York. 942 p. U. S. WEATHER BUREAU 1954. Manual of marine meteorological observations. Circular M. Ninth Edition. U. S. Government Print- ing Office, Washington. 101 p. SHOMURA, R. S. , and T. OTSU 1956. Central North Pacific albacore sur- veys, January 1954-February 1955. U. S. Fish and Wildlife Service, Spec. Sci. Rept.--Fish. 173. 29 p. SNEDECOR, G. W. 1946. Statistical nnethods. Iowa State College Press, Ames, Iowa. 485 p. SVERDRUP, H. U. , and W. H. MUNK 1947. Wind, sea, and swell: Theory of CHART INDEX ~ 1 Chart numb ;r for month of -- Jan. Feb. Mar. Apr. May June July Aug. Sep. Oct. Nov. Dec. Percentage of winds 20 knots I 6 11 16 21 25 29 32 35 39 44 49 or less Percentage of winds 25 knots 2 7 12 17 22 26 30 33 36 40 45 50 or less Percentage of winds 30 knots 3 8 13 18 23 27 -1' -1/ 37 41 46 51 or less Percentage of winds 35 knots 4 9 14 19 .j_/ .2/ .4/ .6/ -1' 42 47 52 or less Maximum observed winds 5 10 15 20 24 28 31 34 38 43 48 53 — Chart omitted since in only one square (50*-55"N. , 145*-150*W.) was the frequency less than 95 percent. — Chart omitted since all frequencies were 97 percent or greater. 3/ — Chart omitted since in only one square (40'-45*N., 125*-130*W.) was the frequency less than 95 percent. 4/ — Chart omitted since all frequencies were 97 percent or greater. — Chart omitted since all frequencies were 95 percent or greater. 6/ — Chart omitted since all frequencies were 98 percent or greater. 7/ — Chart omitted since only three squares (in the Aleutian Islands - Bering Sea Area) had frequencies less than 95 percent. CHART 2. JANUARY PERCENTAGE WIND 25 KNOTS OR LESS CHART 4. JANUARY PERCENTAGE WINDS 35 KNOTS OR LESS 10 CHART 5. JANUARY MAXIMUM OBSERVED WINDS, BEAUFORT SCALE 8 0R LESS! 0 -40K ) [^ 10 (48 - 55K.) [^9(4I-47K) I I II (56-63K.) 2 (64K.- ) II CHART 8. FEBRUARY PERCENTAGE WINDS 30 KNOTS OR LESS 12 CHART iO. FEBRUARY MAXIMUM OBSERVED WINDS , BEAUFORT SCALE 8 0R LESS( 0 -40K ) [ | I0148-55K.) Q9(4I-47K) [~~] I I 156-63K.) "■l2(64K.- ) 13 CHART II. MARCH PERCENTAGE WINDS 20 KNOTS OR LESS 14 CHART 14. MARCH PERCENTAGE WINDS 35 KNOTS OR LESS 15 CHART 15. MARCH MAXIMUM OBSERVED WINDS, BEAUFORT SCALE Q 8 0R L£SS( 0 -40K.) [MBj I0(48-55K.) Q9(4I-47K,) fn\ I I (56-63K.) "■l2(64K- ) 16 CHART 17, APRIL PERCENTAGE WINDS 25 KNOTS OR LESS 17 CHART 19. APRIL PERCENTAGE WINDS 35 KNOTS OR LESS CHART 21, MAY PERCENTAGE WINDS 20 KNOTS OR LESS 19 CHART 23. MAY PERCENTAGE WINDS 30 KNOTS OR LESS CHART 24. MAY MAXIMUM OBSERVED WINDS, BEAFORT SCALE -50« 8 0R LESS! 0 -40K ) | | I0(48-55K ) Q9(4I-47K.) ( I I I (56-63K.) "■ 12 (64K - ) 140° I 150° 160° 170° _l 180° 170° I 160° I 150° _l 140° 130° I 120° 20 CHART 26. JUNE PERCENTAGE WINDS 25 KNOTS OR LESS 21 CHART 27. JUNE PERCENTAGE WINDS 30 KNOTS OR LESS CHART 28. JUNE MAXIMUM OBSERVED WINDS, BEAUFORT SCALE -50" 8 0R LESS! 0 -40K.) | [ I0|4e-55K ) [\]]9(4I-47K.) I I II (56-63K.1 "■l2(64K- ) 22 CHART 29. JULY PERCENTAGE WINDS 20 KNOTS OR LESS CHART 30. JULY PERCENTAGE WINDS 25 KNOTS OR LESS 23 CHART 31. JULY MAXIMUM OBSERVED WINDS, BEAUFORT [TTx] 8 OR LESS( 0 -40K.1 | | I0148-55K.) Q]9(4I-47K.) [~~1 II 156-63K.) "■l2(64K.- ) 24 25 CHART 35. SEPTEMBER PERCENTAGE WINDS 20 KNOTS OR LESS 26 CHART 37. SEPTEMBER PERCENTAGE WINDS 30 KNOTS OR LESS CHART 38. SEPTEMBER MAXIMUM OBSERVED WINDS, BEAUFORT SCALE Q 8 0R LESS! 0 -40K ) | j I0(48-55K ) Q9(4I-47K.) [~] II (56-63K.) "■l2(64K- ) 27 CHART 39. OCTOBER PERCENTAGE WINDS 20 KNOTS OR LESS 28 CHART 41. OCTOBER PERCENTAGE WINDS 30 KNOTS OR LESS CHART 42 OCTOBER PERCENTAGE WINDS 35 KNOTS OR LESS 29 []v] 8 0R LESS( 0 -40K.) [Fj I0(48-55K) [^9(4I-47K) r^ I I (56-63K.) "■l2(64K- ) 30 CHART 45. NOVEMBER PERCENTAGE WINDS 25 KNOTS OR LESS 31 32 CHART 49. DECEMBER PERCENTAGE WINDS 20 KNOTS OR LESS 33 CHART 51 DECEMBER PERCENTAGE WINDS 30 KNOTS OR LESS 140° _l 150° 160° I 170° _J 180° _J 170° 160° _l I I50° I I40° J 130° I 120' ^0° 34 [v^ 80R LESS( 0 -40K.) Q 10 (48 -55K.) □ 9('»I-47K.) □ll(56-63K.) Tl2(64K.- ) 35 mmmimr ,,,-jimiim ,„ WHSE 01178