The Atlantic Hurricane Season of 1968
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March 1969 225 UDC 551.515.2(261.1)"1968" THE ATLANTICHURRICANE SEASON OF 1968 ARNOLD L. SUGG and PAUL J. HEBERT' National Hurricane Center, Weather Bureau, ESSA, Miami, Fla. ABSTRACT The 1968 hurricane season in the North Atlantic area, considered in its entirety, and synoptic and statistical aspects of individual storms are discussed. 1. GENERAL SUMMARY TABLE1.-Hurricane days, 1954-1968 The two hurricanes and onetropical storm inJune Year Jan. Feb. Mar. Apr. May June July Aug. Sept. Dec. Total Nov. Oct. equaled a record established in 1886.2 While there were __-_________ two other years, 1959 and 1936, with a total of three June 1954 ___.__.__.___._..... _____ ..-.-..... 1 ..". 5 8 16 ___._1 31 tropical cyclones, each is not unique as there were two I955 ___.___...4 ..". .____ _____ ..... ._.._..". 22 28 2 .." ~ _____ 56 1956___._..__. ..-....". ___._ ..... ..". ..-.- 1 9 2 ___..3 ____ ._ 15 storms and one hurricane in those years. Two hurricanes 1957__.____.._ _._._..... ..". __.__..". 3 ..... _.___19 _._._ .._.______ 22 occurring inJune are noteworthy when one considers 1958__.___..._ _.___..... ..". _____ .".. _____ .__._14 16 5 ..____.___ 35 1959 __._....._..... __.._ .-..._.___ ..". 1 2 ..___10 11 .._______. 24 there have only been 20 since 1886. This is approximately 1960___......_ ..-.._._._ .".. .____..___4 2 ____.13 ~ ____ .____ ____. 10 one every 4 yr, rather than two for any one June. In spite 1961 ___......_..... ..-.- ..". ___.._____ ..... 4 ___..'35 9 1 .__._49 1962-...-....- _.__. .-..-..". ___.._____ ..__. _.___ 1 ____. 10 .___~ ._.._ 11 of this beginning, the season ended with a total of only 1963 ___.._.__...________ ..". _._.__.______._ .____ 11 7 23 _____ _____ 41 13hurricane days, except for 1962, the lowest number 1964 __._.___......-..... .____ .__.__.__. _____ ..". 7 33 6 ._________ 46 1965___.._.__. ..... _.___.-..- _._._ _____ .__._ ..-.. 6 '21 3 ___.~ __.__ 30 for two decades and wellbelow the yearly average. See 1966. _________ .__.__.__..____ _._._ _____ 7 8 9 11 10 5 _____ 50 table 1 showing the most recent 15 yr. ____._____ ._.___._.. _____ .____'33 11 ____ ~ _.___44 _._.______ .____ 3 ____. 5 .___. 5 _I___ _____ 13 Synoptic meteorologists areparticularly interested in "" ~"____ why there are deviations in the normal monthly or sea- ..-.-_.__. ..".15 91 23619 111 9 1 486 sonal incidence of tropical cyclones. Wecan, in most situations, recognize planetarycirculation patternsthat 'If two hurricanes arein existenceon 1 day, this is counted as 2 hurricane days are favorable or unfavorable for development. In retro- spect,and aside from the climatology, what transpired in June 1968 is more difficult to explain than the activity unfavorablefor tropical cyclone development,although that occurred in other abnormal months of past years. the May-June change mas a favorable trend. Correlations Specifically, Stark (1968) hasshown negative anomalies duringpast years have been acceptable;this one is for May ranging from 50 to 80 m at 700 mb from the disappointing but certainly not discouraging. Since we GreatLakes eastward to Europe.This anomaly was know so little about pressure change mechanisms in the associated with blocking conditions at higher latitudes Tropics and the causes of cyclogenesis, perhaps June 1968 that resulted in farther-south-than-normal westerlies will provevery revealing to research meteorologists. across the Atlantic. Based upon the work of Ballenzweig The relatively large amount of data and events of this (1957), the preferred pattern for tropical cyclogenesis month shouldbe remembered and studied, not written along the Gulf Coast would depict above-normal 700-mb off without further examination. While this report does heights inthe Great Lakes with astrong positive axis not encompass new basic research on the subject, we will eastward to southwestern Europe. Green's (1968) analyses return to this unusual month with some pertinent obser- of the June datado not show this. Indeed, the June chart vations after some general remarks about the remainder was more similar to what Ballenzweig has described as of the season. ~ Changes in circulation features from June to July were 1 Other contributors include R. €1. Simpson, G. B. Clark, N. L. Frank, J. R. Hope, minor as indicated by Wagner (1968). Since there were R. 11. Kraft, andJ. M. Pelissier of NIIC, and W. C. Conner of the Ncw Orleans Hurricanc Weather Office. no storms, the agreementwith Ballenzweig's typesis 2 Actually, Tannehill (1956) describes the cyclone of June 13-14, 1886,as a hurricane. This would total threehurricanes for the month. Existing data do not prove that it was;very good. however, it may have been a minimal one. The authors choose to accept the judgments The westerlies dippeddeep intothe low latitudes of Of Dum and Millcr (1960), Cry (1965), and Dunwoody (1886). These references indicate theAtlantic in August-frequently below 30°N lat. that this early June cyclone was only of storm intensity. One tropical cyclone in 1959 formed on May 28. This caused geopotential heights in the lower troposphere Unauthenticated | Downloaded 10/03/21 09:30 PM UTC 226 ' REVIEWWEATHER MONTHLY vol. 91, No. 3 Unauthenticated | Downloaded 10/03/21 09:30 PM UTC March 1969 Arnold L. Sugg and Paul J. Hebert 221 to be well below normal over most of the ocean-a pattern the satellite picture shows the presence of isolated and that experience has shown to be unfavorable for develop- tall cumuli nearthe area of minimumpressure which ment. (For example, see Andrews (1968) for an inspection support the research mentioned above. Besides the visual of the anomaly fields.) August produced only one named evidence, figure 3 ispresented to show thevery weak cyclone. This is less than the monthly average for hurri- shear in the vertical at Swan Island, the station nearest canes, not tomention the combination of stormsand the depression. This would certainly seem to support the hurricanes. The relatively quiet month was not surprising. conclusion of Gray (1967)--“. most disturbances from Thepattern remainedunfavorable into September. which storms form are generated from an environment in Posey (1968) states there were below-normal heights at which ahorizontal trade-wind currentis present with 700 mb from the westernAtlantic to the BlackSea. minimum vertical shear.” Similarly, it supports the con- Again, this is not what the forecaster looks for as a favor- clusions of Simpson and Riehl (1958), who had demon- able pattern for the development of the long-trajectory, strated that where “ventilation” exists it acts as a con- Atlantic-Cape Verde-type cyclones so typical of August straintupon the hurricane heat engine (development). and September. In figure 1, note that Ednanever attained Another interesting observation, and surely a clue to hurricane force and failed to hold together long enough the formation of Abby, is presented in figure 4. Here we to make the usual recurvature or landfall. see the unanalyzed data from the so-called “TOE chart” Two conclusions mightbe drawn from thisgeneral (hop of theEkman layer)regularly prepared bythe summary. The first is most obvious and can be stated as a RegionalCenter forTropical Meteorology (RCTM) at good forecasting rule: tropicalcyclone development is not NHC.By inspection,one can easily see the obvious favored by blocking Highs at northern latitudes that produce inflow which is so important. A computation of the radial westerlies and below-normal heights in the midtroposphere at componentwith these data withina radius of 4O lat. midlatitudes and in the subtropi~s.~For the second conclu- produced a speed of 0.8 kt. Thisvalue yields greater sion, we return to the month of June, convergence thanthe threshold radial inflow of 1.5 kt The authors canonly reaffirm what several others have around the Gulf of Mexico (muchlarger radius) which saidbefore, that the environment and its changes near is considered favorable for development by Riehl, Baer, the disturbance or depression are just as important for and Veigas (1962). A second computation was not made; development, if not more so, than the large-scale features however, contrast figure 4 with figure 5. Thelatter is discussed in previous paragraphs.Riehl (1963) has em- the TOE chart for a September depression that persisted phasized that there are two schools of thought and goes for several days;the winds show no net inflow; the on to comment on whether most of the research ‘should depression never developed. For the track of this depres- be done on the “internal factors” or the “external forcing sion and others thereader is referred to the accompanying mechanisms.” In this reference, he apparently thinks the article by Simpson et al. (1969). lattervery important, for he alludes to the influences Damageand casualty figures for the 1968 hurricane produced bythe passing (to thenorth) of midlatitude season are given in table 2. Table 3, presenting hurricane troughs in the westerlies. He postulates external cooling statistics in the United States in less than a century of from this arrangement but is quick to point out “There hurricanes, helps to emphasize the,small amountof damage would be only a few days in each hurricane season when and relatively low loss of life in 1968. formation from external forces was a possibility.’’ The following paragraphs will attempt to flag some of the 2. INDIVIDUAL CASES more obvious internalfeatures of the June storms and HURRICANE ABBY, JUNE 1-13 touch on some of the applied research in progress by hurricane ‘specialists recently assigned to theNational When the 1968 hurricane season officially began on Hurricane Center.