TROPICAL CYCLONES 
The total rainfall in a tropical cyclone is dependent 
upon many factors, including rate of ascent of air in 
the storm area, location of the rain gage relative to 
the storm center, rate of movement of the storm, and 
especially topography. The rainfall averages 5-10 inches 
but varies greatly. Thirty to forty inches have occurred 
where topographical influences were favorable, but in 
other storms precipitation amounts have been less than 
an inch and in one instance only a trace was observed. 
Loss of rain from gages is considerable in high winds; 
in hurricane winds it may reach 50 per cent. 
Some records of heavy rains in connection with tropi- 
cal cyclones follow: 
Baguio, Philippine Islands—46 inches in twenty-four 
hours, 88 inches in four days. 
Silver Hill, Jamaica—96.5 inches in four days. 
Mount Molloy, Queensland, Australia—63 inches in 
three days. 
Réunion, Indian Ocean—47 inches in four days. 
Adjuntas, Puerto Rico—29.60 inches in little over 
twenty-four hours. 
Texas, several instances—22 and 23 inches in twenty- 
four hours. 
In most of the foregoing cases orographic influences 
were pronounced. As a rule a station will not remain 
under the direct influence of a tropical cyclone more 
than two days; therefore, it is doubtful if the tropical 
storm was entirely responsible for the total rainfall in 
all of these cases. In some storms much more rain fell 
during the stage of advanced decay than during the 
period of greatest intensity. 
Radar Bands. In recent years radar has been used 
during aerial reconnaissance to track tropical cyclones 
and to locate their centers. Many of the radar photo- 
graphs have revealed the presence of large-scale squall 
or convection zones spiraling inward toward the center. 
A rather typical example is shown in Fig. 2. This 
photograph was taken at Orlando, Florida, at 0220 
EST on September 16, 1945, when the storm center 
was some 136 miles south of the station. The quasi- 
circular heavy precipitation bands are clearly outlined. 
The lack of such bands in the southwest quadrant is 
real and probably due to the decreased convergence 
normally found in that section of the storm in this 
particular stage of development. Wexler [22] concluded 
from a study of this hurricane and of two typhoons in 
the Pacific that, im these three storms at least, the 
precipitation bands were symmetrical while the storm 
was over the ocean but rapidly developed asymmetry 
over land. Friction over land develops a deformation 
in the pressure and wind fields which also changes 
the distribution of convergence. Between these bands 
or zones there is a thick altostratus or nimbostratus 
sheet from which light rain falls contimuously. 
The exact mechanism of these bands has not yet 
been fully explained. Haurwitz [9] suggests that mter- 
nal wave motion occurring when vertical wind-shear 
is present may lead to patterns very similar to the 
convection patterns observed in the laboratory. If these 
convection patterns are introduced into a circular vor- 
tex attended by general convergence, then the bands 
891 
will spiral inward toward the center. Their width and 
spacing, according to Wexler, will change depending 
on the vertical wind and density gradients and the 
Fie. 2.—Radarscope photograph, Orlando, Florida, 0220 
EST, September 16, 1945. Hurricane center 136 miles from 
station. (Courtesy H. Wexler and U. 8S. Army Air Forces.) 
distribution and magnitude of the horizontal conver- 
gence associated with the vortex. 
The “Eye” of the Storm. One of the most spectacular 
aspects of the tropical cyclone is the central calm or 
“eye” of the storm. At the center of the storm the 
wind rather suddenly diminishes from extreme violence 
to 15 mph or less. At the same time the rain ceases, 
the low clouds may be visible only on the horizon, 
and the middle deck becomes broken and often scat- 
tered. Cirrus and cirrostratus clouds are almost always 
present. In the middle of the “eye,” winds may lessen 
to 5 mph and dead calms have been reported for short 
periods, and the sun or stars may be visible. Observers 
have described conditions in the relatively calm center 
as “oppressive,” “sultry,” and “suffocating,” but this 
reaction is apparently psychological and due to the 
rapid transition from hurricane winds and torrential 
rain to relatively calm and humid conditions. The 
few cases of noticeable rise in the temperature at the 
surface and consequent changes in humidity have been 
explained by insolation or foehn effect. 
Deppermann [2] has tabulated the duration of calms 
for some 59 typhoons as follows: 
No. of Mean duration 
Central pressure cases of calm 
Belowa2(toommen (Gascon 101) heen stsit 4 18 min 
PA tO EI) sade (CEG) 010) Geno nsanes ame 16 min 
27.95-28.35 im. (960.0 mb).............. 5 37 min 
Pe) IPAS thal, (OBI) 19919))h Goudancanencn Ill 32 min 
28.74-29.14 in. (986.8 mb).............. 15 39 min 
29.14-29.53 in. (1000.0 mb)............. 17 64 min 
