CHAPTER III

MARINE METEOROLOGY OF THE GULF OF MEXICO

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MARINE METEOROLOGY OF THE GULF OF MEXICO, A BRIEF REVIEW 1

By DALE F. LEIPPER, Department oj Oceonography, Agricultural and Mechanical College oj Tuas

The best general summary of the weather overthe Gulf of Mexico in nontechnical language isprobably that prepared by the United StatesWeather Bureau for the United States Coast Pilot(1949).2 There are a number of articles on thegeneral circulation of the atmosphere and onmeteorological processes without specific referenceto the Gulf of Mexico which, nevertheless, pertainto this region as well as to all similar regions. Itwill not be attempted to review such articles inthe present summary. Two references of this typeare Holmboe, Forsythe, and Gustin (1948), andByers (1944). In addition, there are some publi­cations such as Riehl (1947) which deal with thegeneral weather in the low latitudes and arehelpful in understanding the Gulf of Mexicoweather more completely.

EXTRATROPICAL CYCLONES

Saucier (1949) has analyzed the frequency andbehavior of extratropical cyclones originating onor near the northwestern coast of the Gulf ofMexico over a 40-year period. These cycloneshave marked effect upon the weather of the Gulfas well as upon that of much of the eastern UnitedStates. They occur on the average about 10times per year with a maximum number of 19occurring in 1899 and a minimum of 2 in 1916.The high frequency of these storms appears toresult from the influence on the general circulationof the warm moist surface provided by the Gulfof Mexico, the cold continental air to the north,and the mountains to the west. It was found thatthe cyclones seldom occurred immediately aftera deep cold air mass penetrated the entire Gulfof Mexico but were most common when it remainednorth of the Gulf coast. The storms may beginas early as October. The maximum numberoccurs in January. Very few occur later in the

1 Contribution from the Department of Oceanography of the Agriculturaland Mechanical College of Texa.q. Oceanographic Berles No. 20. Based Inpart upon work done under the sponsorship of the Office of Naval Researchand the Air Force Cambridge Research Center.

I References are listed at the end of the chapter.

spring than April. The regions of formation,directions of motion, and the characteristics of theintensification of the 388 cyclones studied arediscussed.

THE GENERAL AIR CIRCULATION ANDSOME OF ITS CONSEQUENCES

The Bermuda atmospheric high pressure celldominates the circulation over the Gulf, partic­ularly during the spring and summer months.In the late summer there is a general northwardshift of the circulation and, as shown in figure 17,the Gulf comes under the more direct influence ofthe equatorial low pressure belt. The constancyof the Bermuda high tends to maintain steadycirculation and to govern the climate during thesummer. Summer conditions are illustrated infigure 18. No isotherms appear for average watertemperature (sea surface temperature) since thewaters are nearly uniform at about 84° F. asillustrated in the chapter on physical oceanog­raphy.3 The air temperatures on the average arealso quite uniform and high. The southerly posi­tion of the Bermuda cell brings about the south­east-northwest orientation of isobars across theGulf and leads to a predominance of southeasterlywinds, as shown by wind arrows. The windstend to become more southerly in the northernpart of the Gulf. In this region there are prac­tically no northerly winds in summer and only arelatively few from the east or the west. Inthe more southern parts of the area the predomi­nance of the easterly and southeasterly flow iseven more marked.

With a typical summer circulation in the Gulfand the uniform average sea surface temperature,there would be expected only a minimum numberof local weather features over the water whichare the type caused within the Gulf by air flowtoward successively warmer or cooler water sur­faces. However, on a larger scale the relatively

I See Physical Oceanography of the OuIr of Mexico. p. IlY.

89

90 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

FIGURE l7.-Normal sea level pressure, October.

high temperature of the Gulf of Mexico waterscompared to those of other water surfaces in thesame latitudes brings about such a great warmingand increase in the moisture content of the over­lying air masses that weather patterns of the areaare markedly affected. (The mean annual sur­face temperature of the Gulf is 78° F., while thatof a comparable region at the same latitude inthe western Atlantic is 76°, in the eastern Atlantic73°, and in the eastern Pacific 68°).

Typical features of the winter circulation arcshown in figure 19. Here the winds arc more f1'l;mthe easterly directions with fewer southerlies butmore northerlies. There are very few winds fromthe west or the southwest. The sea surface tem­perature pattern shows a variation from morethan 75° F. in the southeastern portion to less than65° in the northwest. Southeasterly winds bringwarm, moist air from lower latitudes and carry itfrom warmer toward colder water in the Gulf.When this flow is slow and sustained, the cooling

by the ocean surface leads to condensation andfog and stratus formation in the northern Gulf.

A discussion of the uppe.r ail' circulation for theGulf llihd Caribbean area is given by Ema andRudolf Penndorf (1944).

AVERAGE CONDITIONS

Average sea-level atmospheric pressures 111 theGulf vary from 30.00 to 30.]5 inches of mercury.There al'e wide deviations from these averages inindividul1l synoptic situations. Worthy of noteis the rliunlo,l pressure variation with a lesserearly morning minimum followed by 0, greaterlate morning mo,ximum o,nd evening minimumand 0, l-'sser nocturnal maximum.

The Atlas of Climatic Charts of the Oceans,published by the United States Weo,ther Bureau,and the Pilot Chart of Central American Waters,published by the Hydrographic Office of theUnited States Navy, issued monthly, give furtherinformation about the winds, pressurcs, tcmpera-

GULF OF MEXICO 91

tures, and other weather features of the Gulf ofMexico. The I1verage wind velocity varies from6 to 8 knots in the summer, with the stronger windsin the southeast portion, to 10 to 12 knots withconsidemble variability in the winter, the higheraverages being in the northeastern portions.

Fog is most frequent in midwinter when ashigh as 10 percent of all observations record lightor dense fog in the north central pl1rt of the Gulf.

In this season fogs occur less tbl1n 1 percent of thetime in the southel1stern portion.

For the year-round the I1verage cloud-coverover the Gulf is '{a to YJo of the sky obscured.In winter and spring the areas most obscured I1rein the north I1nd northwest, while in the summerI1nd fl111 the southern I1nd southwest pOl"tions havethe highest avemge cloud cover. The mostcommonly reported low type clouds I1re cumulus

I"

.0'..'JULY

__ AVERAGE SEA LEVEL PRESSURt. (INCHES)

__ AVERAGE AIR TEMPERATURE (OF)

1zolI.,,4--r'----::,l\------+-----""""""-------f-7't---"7.L-r ---"7.L--.r--f---------1I-----------="'""-.l20

WIND: ARROWS FLY WITH THE WIND. LENGTH 0' """OW GIVES PERCENT OF TOTAL OBSERVATION, TO

SutTEE" POINTS 0., TH! COMPA,S. BAR8S SHOW FORCf ON BEAUFORT SCALl, FIOUfIl[ IN CENT!:R

0' CIACL! GIVES PEACEHTAO[ OF LIOHT, "ARIABLe: WINO'.

o 10 ~ ~ 40 50 60 ro ~ 10 ~oI

SCALE OF WIND P£RCEHT'AOIES

FIGURE lB.-Average sea level pressure (inches) and average air temperature (OF.), July.

92 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

JANUARY

__ AVERAGE SEA LEVEL PRESSURE (INCHES)

__ AVERAGE AIR TEMPERATURE (0 Fl_____ • AVERAGE WATER TEMPERATURE (OF)

WIND: ARROWS FLY WITH THE '#fIND. Lf.NGTH 0' ARROW QIV[S PEfllCEHT OF TOTAL ODSERVATIOHS TO SI)CTI!.ENPOINTS OF THE tOWPA,S. BARBS SHOW FORCE ON BEAUf"ORT 6CAl.E. FIGURE IN CEMTER OF CIRCLE GIVESPEACENTAG( 0' LIGHT, VARIABLE WINDS.

a 10 ~ ~ ~ ~ ~ ro ~ ~ 100

I I S~ALE ' OF WIH~ F'E!RCE~TAG~5 I ,

FIGURE 19.-Average sea level pressure (inches), average air temperature (OF.), and average water temperature (OF.)

January.

which have the greatest frequency-greater than30 percent of all observations-in the summer andfall in a band extending from the Yucatan Channelnorthwestward across the Gulf. Altostratus andaltocumulus are common the year-round, theiraverage frequency being from 10 to 20 percentthroughout the Gulf. In the summer and fallcumulonimbi are observed about 10 percent ofthe time in the western and northwestern regions.

The period of lowest occurrence of rainfall overthe open water is in the spring when less than 5percent of the observations show rain accordingto the Atlas of Climatic Charts of the Oceans.The remainder of the year the frequency is 5 to10 percent over most of the Gulf except for anarea around the Yucatan Peninsula where fre­quencies drop below 5 percent in the winter andsummer. A study by Kloster reported in the

GULF OF MEXICO 93

Coast Pilot shows rain in from 13 to 21 percentof the hourly observations available for the entireyear between 22~0 to 27~0 N. latitude and 80°to 90° W. longitude. Rainfall was most fre­quently reported in the mid afternoon-19 percentversus 15 to 17 percent at other times of the day.

The average depression of the wet bulb is 30 F.for the fall quarter-September, October, andNovember. During the remainder of the yearit is 2° for the western Gulf and 3° for the eastern.

In the summertime the air and the sea surfacediffer in temperature by less than 1°, the seatemperature being higher according to the Atla'sof Climatic Charts of the Oceans. In the falland winter differences increase, with the seatemperature being as much as 5° higher than theair temperature in the area just west of theFlorida Peninsula. This leads to heating frombelow on the average and explains the high fre­quency of cumulus-type clouds over the Gulf.Monthly average sea surface and air temperaturesare tabulated in the chapter on physical ocean­ography (p. 119).

WEATHER OBSERVING STATIONS

It is the purpose of this summary to discussweather over the water in the Gulf. Since theobservations here are sparse.. some of the conclu­sions are drawn from observations made on thesurrounding land areas. The weather observingstations in these areas are shown in figure 20.Those on the coast are listed in table 1. A par­ticularly interesting feature of the Gulf is that

TABLE I.-Weather observing stations along the coast of theGulf of Mexico

Station Location Btatton LO<'.lItionnumber numtK>r

,~I.-._ .. Key WestyFla. (NAB). 642._ •••• Nautla, Verarcuz.211. ..... Tampa. lao (Interna- 692._._._ Veracruz, Veraeruz.

tlonal AIrport). 741.. __ ._ Coatzacoalcos, Veracruz.214.. ..• _ TallahllSSOO

lFla. (Dale 743._ ..•• Villa Hermosa, TabllSOO.

Mabry F cld). 746....• _ Cludad Obrclron. Ta-~...... APalachIcOla! Fla. basco.222_. __ ._ Pensacola, F a. 749.. _.• _ Cludad del Carmen,223•..••• Mobile, Ala. Campeche.231.- .... New Orleans, La. 69L ••.. Campoohe, Campeche.232..••. _ Burrwood, La. 643.. _... Merida, YucatAn.240••••.• Lake Charles, La. 648__ ••.. Cozumel, ~ulntana Roo.241. ...• _

~~J~~~~u't~~x.751_ .. _.. Chctumal, ulntana Roo.

242••••.• 601.- __ .• Swan ISland, West Indies.243... _.. Houston, Tex. 395_._ ... Vcrnam Fie d, Jamaica.2M.. _.•. Victoria, Tex. 397__ ... _ Kln(lllton. Jamaica.2.51.- .. __ Corpus ChrIstl, Tex. 32.5_ ••.• _ Havana, Havana (Casa260..•... Brownsville, Tex. Blanca).491.- .... Cludad VIctorIa, Tamau· 244.. .... Clenluellos, Santa Clara.

Jlpas. 366....• _ Camaguey, Camaguey.349..••. Cludad Camargo, Tam- 367._ •.•• Ouantanamo, Orienta.

aUllpll!l. 2M....•. AntlllR, Orlento.639...... Tuxpan, Veraoruz.

although it covers some 700,000 square miles, itis more than 90 percent surrounded by land. Therather complete coverage of weather informationaround its perimeter makes it an unusual naturallaboratory in which to study changes in thecharacter of air masses as they pass across thelarge body of water.

TYPICAL UPPER AIR SOUNDINGS

A comparison of the upper air soundings fromSwan Island, south of the Gulf, with those ofNew Orleans and Brownsville, on the north andnorthwestern coasts, illustrates the modifyingeffects of the water surface. Monthly averageradiosonde observations for a summer monthand a winter month at each of these stations areshown in figure 21. It will be noted that the an­nual change in structure at Swan Island, which isalmost completely controlled by oceanic factors,is very small, the most noticeable change· beingthe higher relative humidities in the summer.At Brownsville and New Orleans the sea surfaceis cooler in winter, but, also, the continentalinfluence tends to make winter temperaturesdefinitely lower than those in summer.

A rather complete discussion of the tropicalGulf air mass is given by Willett (1943). Hestates that the uniformity of the water tempera­ture in the source regions 'of tropical maritime airmasses has proved to be of more importance infixing the properties of the masses at all levelsthan has the previous life history of the individualair masses. Evidence is given demonstlating thatthe structure of the lower stratum of the air massresults from the turbulent mixing of saturated air.The air masses are characterized by markedpotential instability, implying that all convectiveor mechanical turbulence up to at least 5 kilo­meters elevation must effect an upward transportof latent heat. The high relative humiditiesindicate that active convection extending abovethis level can be initiated by very little verticaldisplacement. Summer thunderstorms are morelikely along the eastern part of the northernGulf coast than along the western. There arehigher relative humidities in the eastern area.

Using a series of atmospheric temperature andmoisture soundings to 45 feet elevation made at4-hour intervals in March 1949 from an oilplatform in the northwestern Gulf, Gerhardt

(PI - INDICATES THAT OBSERVATIONS OF' THE SPEED AND DIRECTION

OF THE UPPER AIR ARE TAKEN.

"'.l....U1

~tzj::tI0-<

ttl0t"t"tzj~....Z0"'.l

~

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"....U1

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~....t"t:tt"...."'.ltel

U1tzj::tI<....0tzj

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ITl -INDICATES THAT UPPER AIR SOUNDINGS OF TEMPERATURE,

PRESSURE, AND MOISTURE CONTENT ARE TAKEN.

O(PT)>01

SlO

65'

0 c:.eTif >23 ~I330

~s~e .'- H:>-3\0 0- 699

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L \ 0, -----.J.10(PI ....u)246 0 \VKSJAIfr \,~. 0~ /""230

, t'

\ .<EX i\ 0 I Mea/ l..._Cl_

/ 8<5"SUUPAH

'CT'''6NW'C

~lPJ 2.,LFl(0

i BYT0

z?/PIi'?i,,

FIGURE 20.-Weather observing stations, Gulf of Mexico area.

GULF OF MEXICO 95

400,--__=.SW:..:.A:::::N:.:...rI=.S.:::.LA:::::No.:.:D::..t...:W::;...:.:I.'--_..,.-..!.:N""E.:..:W_O::.:R..:.:L"-.'E::..:A::..:.N'-"S'--,........ --,- ----'B"-!.R'-"O'-"W~N'-"SrV-'-'1L=-'L:=E'-- ~-----,

30

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1030

88%

-1010

hi

M

10 30-10

-fO

Legend

,,~6Z%,,

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/ C

\ 71°/('BOOt------1--------+-h---;..,.-ollT----+----b-----b'-'-"--f-------f--l,~--h'"''-'''-----+-------i,

\,\,

WINTER \81%SUMMER ------- 83% \

RELATIVE HUMIDITY \

1000f---1

N_P_E_RC_E+-N_T ----+ -\-\+---+ -=~....-+_-.¢8!!..:4!..101.L---+----!!!..L:lSl!>---.q.:...~----4! 83% b880

Mb 0C_

FIGURE 21.-Average radiosonde observations from selected stations in the Gulf of Mexico area.

(1951) demonstrated the modifying effects of thesea surface. He was able to support the usuallyassumed logarithmic distribution of water vaporwith height, the variation of the evaporationcoefficient with wind speed and the essentialsimilarity of the heat and moistme transferprocesses.

A discussion of the extent to which the seasurface affects the overlying atmosphere is givenby Jacobs (1951). He computes the averagewinter evaporation in the Gulf to be of the orderof 0.40 gms. per cm2/day and compares this withthe other ocean areas of the world. Similar com­parisons are made for the other energy exchangeprocesses operating between the sea and theatmosphere.

NORTHERS

A period of north winds lasting from 1 to 3 or4 days and having speeds greater than approxi­mately 20 knots is known to seamen as a"norther." Each year 15 or 20 northers areobserved in the Gulf, usually between Novemberand March. Many of them reach as far south asKey West, Florida, and Tehuantepec, Mexico.The low temperatures of the polar air masses

which move in and the large waves built up in theopen Gulf have considerable effect upon shippingand work at sea. Also, the water level is oftenlowered in the shipping canals and in harborsalong the north coast markedly affecting shiptransportation in the area. According to theCoast Pilot a veering of the north winds into theeast and southeast brings a resumption of fairweather, while a backing toward northwest meansmore foul weather.

METEOROLOGICAL TIDES

Water levels along the coasts of the Gulf changenoticeably with changes in wind speed and direc­tion. Two extreme conditions are the changeassociated with a norther, mentioned above, andthe storm tide associated with a hurricane anddiscussed later. However, the stress of the windacting upon the sea surface at times other thantimes of northers or hurricanes may also be suf­ficient to bring about a water level change of thesame order of magnitude as that resulting from theperiodic tide-producing forces. This leads toconsiderable deviation of the observed waterlevels from those published in the tide prediction

96 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

manuals. It does not mean that the manuals arein error but rather means that a non-periodic,usually short-term wind effect must be super­imposed upon the published predictions. One ofthe most challenging problems facing the meteor­ologist-oceanographer is that of finding a way tocalculate these wind effects for different situations.Some work has been done by Dietrich (1937).

HURRICANES

The Galveston flood tide of 1900 in which6,000 persons lost their lives emphasizes the impactof the Gulf coast hurricane upon that region.Much has been written on this and similar storms.Some references are the Coast Pilot, Tannehill(1944), Cline (1926, 1933), Riehl and Burgner(1950), and Shisler (1949).

Nearly 80 percent of the hurricanes appearingin the Gulf form outside and enter moving north­westward across the Yucatlm Channel and FloridaPeninsula area. Approximately 15 percent formin the northern Gulf, and most of the remainderform in the southwestern Gulf. They travel atan average speed of 10 to 13 knots. The mostcommon path is westward becoming northwest­ward and northeastward. Some, however, donot turn northward. The months of greatestfrequency and intensity are August, September,'and October. There are an average of about ninehurricanes each year in the western North Atlantic,and many of these enter the Gulf.

Hurricanes are usually 100 to 500 miles indiameter. In the eye of the storm is a region ofcalm where the water level rises in a "hurricanewave" which may be 20 feet or more in height.Around the storm center, high-wind wavesdevelop. Passing out of the wind area thesewaves become swells and often provide the firstindication that a hurricane is approaching.

Much of the damage caused by hurricanes incoastal areas is due to the fact that the wind­driven storm tide raises the water level sufficientlythat the high breaking wind waves are carriedacross breakwaters and retaining walls into un­protected inshore areas. The tracks of the centersof hurricanes which caused the highest tides ofrecord on the Gulf coast are shown in figure 22.A detailed discussion of such meteorological tidesis given by Cline (1933).

In recent years much has been learned aboutthe formation and motion of hurricanes from theweather flights into the centers of the stormsmade by the United States Navy and otherflights made by the Air Force. In addition, thestorms have been followed by radar sets, sincethey make a distinctive pattern on the radarscreen.

APPLICATIONS OF MARINEMETEOROLOGY IN THE GULF

The heavy investments by the petroleum in­dustry in the shallow waters of the Gulf (some250 million dollars) are greatly affected by mete­orological conditions as evidenced, for example,by a symposium on this and related subjectsappearing in the February 23, 1950, issue of theOil and Gas Journal. Glenn (1950) discusses theplace of meteorologists in improving the safetyand efficiency of offshore petroleum operations.

The many large industrial organizations on thecoast need information about offshore weatherfor use in conducting their oper.ations. Severalorganizations have established weather observa­tion stations including radar facilities, such asthose described by Jorgensen and Gerdes (1951).

Fishing here, as elsewhere, is successful or notdepending to a large extent upon the weather.Navigation, protection of beaches, constructionalong the coast, and recreation all furnish applica­tions for knowledge gained in the study of marinemeteorology.

FURTHER SOURCES OF INFORMATION

Many pertinent articles on marine meteorologyare reproduced on the back of the Pilot Charts.An index to those between January 1946 andSeptember 1950, inclusive, appears on the chartfor November 1951. Some examples are: Cyclonicstorms-October 1949, Fog-September 1946,Hurricanes and Tropical Disturbances-August1946, 47, and 48, Northers-September 1949, 50,and 51, Line Squalls-March 1948, Northers­September 1947 and November 1948, Water­spouts-December 1948, and the Gulf Stream­August 1950. These charts md.Y be obtained for30 cents each by addressing a request to theUnited States Navy Hydrographic Office, Wash-ington 25, D. C. .

GULF OF MEXICO 97

FIGURE 22.-Tracks of centers of hurricanes which caused highest tides of record on the Gulf coast. (Tannehill).

Geyer (1950) includes a number of references tothe marine meteorology of the Gulf.

CONCLUSION

The development of marine meteorology in theGulf of Mexico and other ocean areas has beendelayed by the lack of sufficient information aboutthe underlying water surface which exerts a dom­inating influence upon the atmosphere. Onlyrecently has there been increased emphasis uponthe collection of this information and upon theanalysis of the data in such a manner as to leadto more complete understanding of the processesof interaction between the sea and the atmosphereand their effect upon the weather.

LITERATURE CITEDBYERS, H. R.

1944. General meteorology. 645 pp. McGraw-HillBook Co., Inc.) New York.

CLINE, 1. M.1926. Tropical oyclones. 301 pp. The Macmillan Com­

pany, New York.1933. Tides and coastal currents developed by tropical

cyclones. Monthly Weather Review 61: 36-38.DIETRICH, GUNTER.

1937. 1. Die Lage der Meeresoberfliiche im Druckfeldvon Ozean und Atmosphiire, mit Besonderer Berucksichtigung des Westlichen Nordatlantischen Ozeansund des Golfs von Mexiko, Veroffentlichungen desInstituts fUr Meereskunde an der Universitiit Berlin,Neue Folge A. Heft 33, 91 pp., January.

GERHARDT, JOHN R.1951. Temperature and moi ture soundings over the

Gulf of Mexico for March, 1949. Trans. Am. Geo­phys. Union 32(1): 15-25, February.

98 FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE

GEYER, R. A.1950. A bibliography on the Gulf of Mexico. Tex.

Jour. Sci. 2(1): 71-76.

GLENN, A. H.1950. Wave, tide, current, and hurricane problems in

coastal operations. Oil and Gas Jour., June 22.

HOLMBOE, JORGEN, GEORGE E. FORSYTHE, and WILLIAMGUSTIN.

1948. Dynamic meteorology. 363 pp. John Wiley andSons, Inc., New York.

JACOBS, WOODROW C.1951. The energy exchange between sea and atmosphere

and some of its consequences. Bull. Scripps Inst.Oceanog., Univ. California, 6(2): 27-122.

JORGENSEN, R. C., and W. F. GERDES.1951. The Dow Chemical Company leads industry in

using radar for hurricane detection. Bull. Am.Meteorol. Soc. 32(6): 221-225.

PENNDORF, ERNA, and RUDOLF PENNDORF.1944. Aerologische Studien nr. 7. Die Stromungs­

verhlUtniss in der freien Atmospharc-besonders diedes passates-uber dem Karibischen Moor und demGolf von Mexiko. Ann. Hydrogr. 72: 106-116.Berlin.

RIEHL, HERBERT.1947. Subtropical flow patterns in summer. Misc.

Rep. No. 22, Dept. Meteorol., Univ. Chicago.

RIEHL, HERBERT, and NEWTON M. BURGNER.1950. Further studies of the movement and formation

of hurricanes and their forecasting. Bull. Am.Meteorol. Soc. 31 (7): 244-253.

SAUCIER, WALTER J.1949. Tcxas-west Gulf cyclones. Monthly Wcather

Review 77: 219-231.SHISLER, KARL.

1949. Maintcnance of safety and cfficiency in offshoreoperations during periods of hurricanes. Oil andGas Jour., Junc 30.

TANNEHILL, IVAN RAY.1944. Hurricanes. 269 pp. Princeton Univ. Press.

U. S. COAST and GEODETIC SURVEY.1949. United States Coast Pilot, Gulf coast, Key West

to Rio Grande. U. S. Dept. Commerce, 3rd ed.,Ser. No. 725, pp. 50-83, U. S. Govt. Printing Office.Washington.

U. S. HYDROGRAPHIC OFl"ICE.Pilot chart of the Central American waters. Issued

monthly by the Hydrographic Office of the U. S.Navy' Dept., H. O. No. 3500. Washington.

U. S. WEATHER BUREAU.1938. Atlas of climatic charts of the oceans. U. S.

Dept. Agriculture, W. B. No. 1247. Washington.WILLETT, H. C.

1943. American air mass properties. MassachusettsInst. Tech. and Woods Hole Oceanog. Inst., Papersin Phys. Oceanog. and Meteorol. 2(2): 1-116.