TROPICAL CYCLONES 
oscillations. Deppermann, upon examining all Philip- 
pine barograms of tropical cyclones found [2]: 
No. of 
cases 
1. Traces with no oscillations observable............ 143 
2. Traces with only long-period oscillations or with 
long-period superimposed on short-period. . 79 
3. Traces with only long-period oscillations (10-30 
TAD) 5 ceed noe PA Tee DOO oO RIE one ae 21 
4. Traces with doubtful oscillations, 7.e., doubtful 
Glas 1@ lols AyaGl JONES oon eaucaccocnbageeoagasas 25 
5. Traces which possess, almost surely, only oscilla- 
ioussolveny small perlods ... gens o ss see oe an 2 
He concludes that, for the Philippines, short-period 
oscillations are the exception rather than the rule. This 
has also been considered true of the Atlantic. However, 
most barographs are designed to damp out minor short- 
term oscillations. 
Deppermann found evidence of long-period oscilla- 
tions in 100 out of 270 barograms with minima under 
29.14 inches. He states that the simplest and most 
clear-cut cases resemble very much in form and period 
the oscillations on the microbarograph when there are 
thunderstorms quite near but not actually over the 
station. 
No generally accepted explanation for these oscilla- 
tions has been advanced. Short-period oscillations may 
be due to the pounding of the long hurricane swells on 
the beaches, strong rhythmic gusts of the wind, and 
the effect of gusts on buildings including the swaying of 
tall buildings. Long-period oscillations may be due to 
the regular march of intense squalls around the storm. 
In the most intense storms, violent pumping of the 
barometer may occur near and in the storm center. 
Violent kinks in the barogram are occasionally ob- 
served. In the July 1943 hurricane at Galveston, Texas, 
the Weather Bureau City Office barogram contained 
a kink just before and another just after the barometric 
minimum, but neither appeared on the barogram at 
the airport five miles away. 
Temperature. At the surface no change in temper- 
ature is noted with the approach and passage of the 
tropical cyclone other than the lowering of the free air 
temperature to or near the dew-point or wet-bulb tem- 
perature incident to the heavy rain. 
Wind Circulation. Winds in tropical cyclones of the 
Northern Hemisphere blow counterclockwise around, 
and incline inward toward, the center of the storm. 
However, the degree of incurvature toward the center 
is not uniform in the various quadrants. Cline noted 
that there is a systematic difference in the inclination 
of the winds in the four quadrants, and others have 
attempted to calculate the exact degree of incurvature. 
However, it appears that the incurvature varies con- 
siderably with individual storms and with their stage of 
development, size, latitude, and other factors. The 
winds in the right rear quadrant usually blow more 
directly toward the center (greatest incurvature) than 
is the case elsewhere. The intense storms of the im- 
mature stage have the most symmetrical circulation. 
While there is some lack of uniformity from one storm 
to another with regard to winds in the right front quad- 
rant, they usually appear to move directly across the 
889 
line along which the storm is moving and are tangential 
to the isobars. However, more definite information is 
needed on the surface circulation, the cross-isobar com- 
ponents, and the field of convergence. 
If a hurricane is moving between west and northwest, 
the most commonly experienced wind along the line 
over which the central calm will move, preceding the 
calm, is north or north-northeast, usually the latter, 
and the wind may blow from this direction for hours, 
without veering or backing, prior to the arrival of the 
storm center. If the wind tends to veer or back, the 
center is unlikely to pass over the station. If the storm ~ 
is moving in a northeasterly direction, the most usual 
wind preceding the arrival of the storm center is north- 
northeast to east-southeast. 
The wind velocities encountered around the storm 
are affected by the stronger pressure gradient usually 
present to the right, since in westward-moving storms 
the semipermanent subtropical high is to the right and 
the intertropical trough to the left. Thus gales and 
hurricane winds extend farther to the right than to the 
left. In intense immature storms velocities increase until 
a few minutes before the calm, but in the mature and 
decaying stages the highest winds may occur as much 
as two hours before and one hour after the central calm. 
The dimensions of the hurricane winds will vary with a 
number of factors: maturity of the storm, pressure 
gradient, central pressure, etc. In the large Cape Verde 
storms, the diameter of hurricane winds may exceed 
100 miles by the time the storm has reached the western 
Atlantic. 
[= 2 
o ° 
2 = 
(o) Eo 
S) nw 
Ty} a2 
o Zz 
~ 26 
> >o 
990 
MILLIBARS 
MILES PER HOUR 
5 50 
MILES —> 
VR = CONSTANT 
RADIUS (MILES) |30|40]50 | 60|70 | 80/100/200 
VELOCITY (MPH) [100] 75 [60 [50 [43 [37] 30/15 
Fre. 1—Deppermann’s typhoon model. 
In the Labor Day storm in 1935 over the Florida 
Keys, the most intense hurricane in the history of the 
United States, the diameter of hurricane winds was 
