AUGUST 1933 MONTHLY WEATHER REVIEW 223
Year
1909 .........................................
1910 ......................................... 1911 ......................................... 1912 ......................................... 1913 ......................................... 191 4 ......................................... 1915 ......................................... 1916 ......................................... 1917 ......................................... I918 .........................................
1918.. ....................................... 1g20 ......................................... 1921 ......................................... 1833 ......................................... 1923 .........................................
1924.. ....................................... 1Y25 ......................................... 193 6 ......................................... 1927 ......................................... 19. .........................................
1929 .........................................
1930 .........................................
1931 .........................................
1932. ........................................
TABLE 1.-Years of deficient rainfall (percent of normal) i n order of relative dryness, Island of Puerto Rico, 1899 to 193.2
North
Pereeni 108
101 Io6
89 90 93 I17 122
104
67
9s 90
90 91
82
1M 8.i E9 13' 10:
88
76
127
108
-
TABLE 3.-Percentage rainfall departure roin normal b y sections: Piierto Rico, 1899-1992- d ontinued
Perccnt 125
98 107 96 96 94 55 131 89 82
-
[sland
Pereen,
1.18 74
113 1?4 94 91 90 134 81 93
__
West
%cen
lo(
91
103 114 93 106 $9
97 97 99
89 92 101
106
88
88 106 99 114 1 3
92
87
111
110
-
-
-
19?5
19% 1Y30 1021 1807
84 1907 E5 1818 R7
i8 1915 85 1930 85
73 1910 74 1923 75
88 1915 h9 1915 69
85 1939 85 192.5 88
89 96 99 95 72
110
88
78 117
109
-
ion 1M 57
72 75
111 80 65 104 132
105
85
121 - 143
2 72
143
124
North ........... East.. ..........
West ............ Islnnd ..........
south ...........
pp_______--___
73 5 1901 134 192: IR? 1931 127 1916 I?? 1915 117
75.2 1931 143 1901 137 1909 125 1916 131 1932 121
7fi 9 1928 1% 1901 I ?i 1927 114 1912 114 1931 111
67 1 I le01 131 1931 1% 1916 121 192: 120 1902 118
42 o le09 198 1531 143 ign? 13s 1916 1x1 imn 133
Per- cenl 131
18 66
E7
175 145
81 94 155
103 84
104
108
Inchel 4.62 1.44 3.40 6.89 10.02 10.65 11.13 9.17 9.58 9.63 7.82 6.46
80.81
hchcs 4.28 .71 2.44 4.30 11.96 7.58 6.07
7.96 11.28 7.21 6.11
4.83
74.71
Per- cent 121 24 72'
97
188 134 02 117 149 94 85
108
112
Year -
18. ......................................... 19 oo...... ................................... 1901 .........................................
19oa ......................................... 1903 ......................................... 1804 ......................................... 1 ~5 ......................................... 1806....... .................................. 1807.......... ............................... 1908. ........................................
North
Percent 110 101 134
115 94 93 94 96 85 93
- 138 107
109 109 97 80 96
106 103 109 93 98 94 93
East South
-- -
Percent 116
95
107
loa 91 89
lo? 121
07 51
97
(14
92
Sn
SO
105
R9
80 130
I14
88
79
123
112
-
hTorth .......... 73. 5 1930 76 1923 83
South.. ........
1
42.0 1929
I !$ 1 ;;;; 1
72
Island: _______ __. 67.4 1930 79 1933 YO
East ........... i5.28 1923 I907 7.1
West ............ 76.9 1930 ss
section
1
Mean
r l ~
Per-
Year ::; Pear cent
I- 1-1-1--1- 19?6 89 1913 90 igzn yo
1 9 3 92 ign5 93 I Y ~O 92
1918 O? 1914 Y4 1Y11S 94
1917 81 1921 6 i lY2R SS
1913 91 1921 92 1 9 3 94
North East
west
I I I 1 I
Note: Old Spanish records, Ean Juan, dating from 1868 show a dry period, approxi- matin? the record for 65 years in 1Yi3, annual rainfall 68 percent of the normal and in 1893 67 percent of normal. Cnnoranas record lS9fl-98 also hm record dry penod. 1693 68 per-
cent.
TABLE 4.-Percentage of the average precipitation i n the S years of
deficient and the S years o f greatest precipitation in the groups of States, no. 1 to 4 , and in Puerto Rico
TABLE 2.-Years of greater than normal rainfall (percent of norinalj i n order of relative depth, Island of Puerto Rico, 1899 to 19%
I
Least Greatest
Groups Range
No. 1 ................................... No. 2 ................................... No. 3 ................................... No. 4 ................................... Puerto Rice..-. ........................
TABLE 5.-Coinparative data on the rainfall i n Puerto Rico during 1968, by sections, inches rainjall, and percent of normal
North ..................... 1802 115 1689 110 1909 108 1932 106 1928 107 East ....................... 1903 120 1905 I17 1927 117 1904 1lS 1 9 3 110
South ..................... 1912 134 1932 124 1899 123 1928 122 1901 118 West ...................... 1032 110 1904 108 1699 108 1914 106 1903 106
Island .....................
1 i i I l l i !i I l
1909 115 1926 114 1933 112 1899 110 1911 107
I North 1 East South West
-
Per :en1 71
26 97 107 3 3 190 60 164
118 65 1M 174
124
-
-
Per- Cent 111
28 63 85 180
68 1M 129
182 100 69 68
110
-
-
Per.
:cnt
121
42 103 181 149
148
153 128 104
102
8.3
121
i a i
-
TABLE 3.-Percentage rainfall departure from normal b y sections: Puerto Rico. 1899-1932 -
Island
Percent
IM 131
119 98 101 lo0 96 85 94
-
i i n
-
Inchca 6.36 .67 2.71
4.34 11.70 8. 26
5.90 6.46 11.57 7.21 6.80 6.38
78.36
Inchca 1.02 .48 1.63 2.60 10.60 6.98 2. 25 7.58
6.69 4. M 4.85 3. 14
52.02
'nches 2.60
.70 2.29
5. M 14. 23 5.02 8.79 11.76 17.11
9. 75 5. 11
2.23
84.63
January. - __ - __ - - - - ._
February _____________ March ______.___ ___.._
April. ................ May. ................ June.. - __ ____ _..____ - July- ____ - - - .._. . - - - August ._---- -- ------ -
September - - - - - __ - - __ October. ............. November--- ._ - -. __ -.
December. ...........
Year ............
__
East
Percrni 102
109 137
120
(59 115 117 96 74 94
-
Percent Pcrcenl 123
I
10s
133 91 118 127
STORM TYPES AND RESULTANT PRECIPITATION IN THE SAN DIEGO AREA
DEAN BLAKE
[Weather Bureau, San Diego, Calif., 19331
At the request of engineers and water conservationists of southern California, who are not satisfied with the
rate and intensity alone of the rainfall but wish also to laow something of its origin, tables were prepared which
segregated storms inSan Diego County into four groups ac- cording to their genesis. Weather maps of the north Pacific Ocean are available in San Diego for only the last 5 years,
hence the data could not be carried back farther than 1929.
From available weather-reporting stations in San
Diego County, 3 were selected, San Diego, 87 feet eleva- tion, Cuyamaca, 4,677; and Warner Springs, 3,165. The
criteria were length and dependability of record, eleva- tion, and surrounding topography. San Diego was con-
sidered as representative of the coastal, Cuyamaca the mountain, and Warner Springs the intermediate rainfall
regimes. Warner Springs m particular is well located for a ra.infa11 study, for i t is surrounded in all directions by nioderately high mountains, and the effects of the
dynamical or a,scensional cooling of the rain-bearing winds here are nearly equal, regardless of the direction from
which they come. On the other hand, the rain gage at Cu- yamaca is exposed in a draw, and records very heavy rains
when winds are from the southwest quadrant. In fact, i t is located at one of the rainy spots of southern California.
From data of the three stations, three tables have been compiled: (1) The total number of days and amounts of
224 MONTHLY WEATHER REVIEW AUGUST 1933
rain froni storms of each type; (2) the number of days, amounts and percentages of precipitation for each of the
five seasons produced by storms of each type; (3) sea.sona1 precipit,ation and departures froni the mean. There is
little differe,iice in the number of rainy da.ys a t tlie stations,
so the figures for Sa.n Diego are mcepted RS represe,ntative of all three. Ot,lier tables were pmpared, among which was
one showing the number of days with four arbitrarily kxed
amounts. At the outset it was realized that the place of origin of
many of the storms would be in doubt, lack of data pre- venting us from tracing their source or their movements
in the early stages of their careers. Four broadly generalized types or groups were immedi- ately apparent. The first, designate.d the nort,h Pacific
type, includes all cases of low-pressure are,a.s t1ia.t' a.p-
proached the mainland froni t,he Pacific Ocean nort'li of Sa.n Francisco. The second, designated 6he south Pacific type, c.omprises a.11 disturbances that came from the ocean
south of San Francisco a.nd nort,li of the Tropic of
Cancer. The third, designated the interior type, con- tains 8.11 active depressions that origina,t,ed or developed over the plateau regions, the Colorado Valley, or the California interior. (An appreciable number of these
were secondary disturba.nces to parent LOWS passing eastwa.rd ne,ar t,he Canadian border or through the Cana-
dian Nort>hwest.) The fourth, designated the Mexican type, consists of the tropical disturba.nces t,hat occasion-
ally moved nort,hwa,rd to southern California from tlie west coast of Mexico, and also, not logically but a.s a mat-
ter of convenience, the few sporadic thunderstorms of the warmer months, know-ii 1oca.lly as " Sonora,s. "
This afforded an index to the rainfall rate.
NORTH PACIFIC TYPE
This group ties in naturally with the recognized and fun- damental typesset forth by Thomas R.Reed? As he stat,es,
his westerly types, which may be associated with the nort,h Pacific type of this pa.per, and have t,he same characteiistics,
"ruc well to the south on many occasions" and when their
paths are more southerly than usual, southern California is found within t,lie precipitation area. This type is respon-
sible, for most of the rainy da.ys, the largest falls, and the greatest number.of days of any given intensity.
The general trend of norther storm tracks is southward
with the approach of winte,r, but not until November is sout,hern California within the precipitation a.rea. The
amount of precipitation and the number of days with rain increase until the maximum is reached in Ja.nuary, after which, with the re,t,urn northward of the storm paths, both become le,ss and end completely in May. It is wort,liy
of nobe that days with rain are about equally frequent
from February to May, while the c,atch falls off materially, de,noting a decrease in energy rather than in the number
of storms. This type appears to be the most dependa.ble of the four. Large excesses and deficiencies in seasonal
totals seem to be due more ofte,n to a.n unusual number of storms of the other types rather than to wide varhtions in
the north Pacific group.
SOUTH PACIFIC TYPE
Apropos of his easterly type, Reed states:
Lows of like origin sometimes form over the southern California coast on t,he tropical side of an overrunning southwest high, or they may lodge there after running south along the eastern flank
of a nort,h-south HIGH which, after t.heir passage, presses inland over t,he Pacific Northwest. in a quasi-enveloping movement.
1 Sonora Storms, D. Blake. Monthly Weather Review, November 1923.
f Weather types of t.he nort.heest Pacific Ocean as related to the weather of bhe north Pacific coast. T . R. Reed. Mo. WEA. REVIEW, December 1932, vol. 60, pp. 346-253.
Lows of this nature are re,sponsible in the main for st,orms c.1assifie.d under t,he soiit'li Pacific, t,ype. At t,inies,
t,liough, disturbances t,hat are associate,d wit,h Reed's southerly t8ype take t,he form of n t,rough, and lie near
enough to the coast to bring San Diego County under the dominat,ion of the secondary depressions that form
in the lower end of the trough. This group is also chssi- fied under the south Pacific. type.
The appeara.nce of storms in this area is haphazard, and wide variations in number and rainfall amounts are
found, but apparently condit,ions are most favorable for their formation during February, a,s they have proved to
be the best rain producers during that month of any of
t,he four t'ypes. They de.ve.lop from November to March, move quickly, travel singly, and produc,e wa,rm and not
infrequently very he.avy rains, part,icularly a t stations
where t)he mounta,in ranges parallel the. c,oast.
INTERIOR TYPE
By far, t,he most, int,eresting and complicated disturb- ances are of the interior type. Storms of this nature cor-
respond t'o those which are t'he result of Reed's nort,herly
typ?. While the.ir bree.ding place appears to be the Great Basin most of the t,inie,, neverthele,ss they develop any-
where over the far weste,rn interior, Their growth and subsequent movemenhs are erratsic and hard to predict wibh any great degree of accurac.y. Before the last
dec.ade the temptation w-as to ignore them as potential heavy rain producers. The tables show that in San
Diego County 32 percent of the tot8al number of rainy days and about 30 pe.rc.ent of the precipitation resulted
from storms assigna.ble to this type, and that 24-hour
amounts gre,ater than an inch we.re fre,quent. Because of t8he large high pressure area over the ocean off the coast of California at the t,iine these LOWS form, too little
w-eight usua,lly is given to bhe drop in barometer that pre-
cedes their genesis, and before we are aware of it, general, and in many cases, heavy rain has begun over all of south- ern California. While interior stornis are most active
from February to May, t,hey may form in any month of the year. During t)he last 5 ye,ars, however, none was
t,abulated during July or January.
MEXICAN TYPE
The fourth and last, the Mexican t8ype, is responsible
for only a small percent of the whole number, but the amounts of their precipitation a t Cuyamaca and Warner
Springs are much greater than a t San Diego, and add materially to the season's totals. Only occasionally do they Cross San Diego County. They originate in the
tropics south and west of Baja California, and move
northward, and only through c,hance radio reports from ships that happen to be in their path are we able to follow
them. Occurring at a t,inie when fruits and grapes are
ripening or drying, they always are most unwelcome.
Torrential rains often are the re,sult, a t which times dam- age to property is gre,at, railways and highways suffering
heavily. An example of particularly destruckive rains of t8his type was the storm in the Tehachipi Mountains of September 25 to Ockober 1, 1932, where the loss of life was 15 and the damage was estimated to be over
$i,000,000.3 Fortunately they are limited to the period from August to November, and years have passed wit,h- out one of serious proportions reaching this part of the
State.
a Destructive rains in the Tehachipi Mountains, Kern County, Calif. M. Gprague, in October 1932 Climatological Data, California section.
AUGUST 1933 MONTHLY WEATHER REVIEW 225
TABLE 1.-Total number of days with rain from each type at S a n Diego, and total amounts from each type at S a n Diego, Cicyamaca, Warner Springs, during the last jive seasons
Days
3 5 7 11
3
N0rt.h Pacific
1
Amounts
0 0 0 0 0 0 0 0 .3 i 1.65 3.46
5 .2
.34
0 0 0 0
0 0 ____
I I I
July. ............... August .............
September.. - -. - ..
October ............
November.. .......
December.. ........ January.. .......... February. ......... March. ............ April ............... May ............... June.. -. -. - - - - -. - ..
Percent. -. -. .
Total.. .___
Cuya- Warner
1 ~a n ~i e g o I maca I springs Month
-
-
106 5o 1 i2S9 I ;J51 1 :;36
I 1-1-
~.
0
0 0 0 10 17 39 11
9 10 10
0 ~.
1 Days I Amounts IAmounts 1Amounts
~-
0 0 0 0 1.66 5.85 11.83 2.05 1.40
.96 .84 0 ___-
--
0 0 0 0 5. 26 23.97 30. CM
13.45 5. 29
7.99 5.51 0 __-
0
0 0 0
1.03 2.9i 13.63 13. 6.Q
2.09
0 0 0
33.40 17
~~-
0 0
0 4
0 1 0 3 .51 6
1.52 3 6.08 0
8.40 10
51 14
0 10
0 4
17.03 6s
20 33
0' 13
--___~
0 .os .M .41 1. 11
.85 0
3.26 3. 11
4.30 1.80 .12
15.08
39
-
0
0 0 0 2.03 6. 78
11.40 4. 62 1.87 3.32
1.35 0
0 0
0 0 .05 . 01
3.52 2.01 6.35 2.60 7.72 3.21
0 0
11.04 6.69 7.65 3.99 12.07 4.03 9.43 5. 26
. 16 .06
57.90 2i.86
29 32
~~~
South Pacific Interior
I
0
.03 .23
1.10 .78 0 0
0
0
0
0
San Diego
1.24 0.38 3.03 5.17 1.94 5.30 5.52 2.95 .63 .41 0 0 0 0
0 0
0 0
0 0
0 0
29 10.w2 14
~
30
hiesican
Days
0
2 2
2 2
0
0 0 0 0
0 0
8
4
__
-~~
\mounts Amounts Amounts
-~- i l
TABLE T-Total number of days with rain and percentages at S a n Diego, and total ainoicnts and percentages from each type by seasons at San Diego, C'uyaniaca, and Warner Springs
NORTH PA4CIFIC
TABLE L-Total nicmber of days ruzth rain and percentages at S a n Diego, and total amounts and percentayes from each type by seasons at S a n Diego, C',icyamaca, m i d Warner Spri~~gs--Continued
MEXICAN
193-29 ............... 25 GO 5.12 73 35.05 70 S.75 71 19%-30. .............. 43 4 01 3; 15.34 37 5.09 25
1930-31 ............... .............
1 3 9 , 4 .4 i i
30.23 8.4'31 321 3.251 8.86 27 36 1931-32. ti. S6 1933-33. ............. 4. 13 3!1 11 $1 5 .3 Y 32
1928-29 ............... 1 2 0.02 0 0 0 0.08 1 5.06 12 3.87 19 15-%30. 193&31 1531-3 ...............
1
0 :z I L A i ! 3:iii I;
1932-33.. ............. 1. 10 5. 52 3.10 18
..............
................
SOUTH PACIFIC
19%29 ............... 1 2 0.10 1 0.73 2 0.28 2 19%-30. .............. 14 1.51 14 8.95 21 4. i 6 23
1930-31 ............... 1931-33 ..............
1 'i 1 !i I
~~~~
1 ii 1 i:g I 1 i?! 1 193M3 ............... 14
INTERIOR
TABLE 3.-Precipitation and departures from the mean ut S a n Diego, Cicyainacn, and Warner Springs during the last five seasons
Warner Springs Cuyamaca San Diego
Season
1938-29 ............... 15 36 1.86 26 5.77 25 3.16 38 19x1-30- .............. 4.99 47 12.30 30 6.89 33
1930-31.. ............... .............
1 I)
3.46 1.891
"1
11.38 9.291
"1
8.66 3.961 34 25 1931-33 1932-33. .............. 2.88 27 15.30 38 6. 19 36
19B-29 .................
1
i. 10 -2.65
1
35.55 193-30 ................. 10.73 +.9S 41.65 193&31 ................. 10.78 4-1.03 2 6 .Z
1931-32 ................. 13.1'3 +3.43 53.58
1932-33 ................. 10.63 +.88 40.14
-3.35 12.30 -5.48 +2.'35 20.61 +2.MB -13.02
I
11.86
1
-5.02 +14. 78 35.14 +i.36 +1.34 17.18 -.eo
HOURLY FREQUENCY AND INTENSITY OF RAINFALL AT SAN FRANCISCO, CALIF.
By R. C. COUNTS, Jr.
[Weather Bureau, San Francisco, Calif., August 19331
[Compare: McDonald, W. F., Hourly Frequenry and Intensity of Rainfall at New Orleans, La. Mo. WEA. REV., January 1929, vol. 57, pp. 1-81
The hourly rainfall data for San Francisco present several aspects, the most interestin of which is the de-
and early morning hours than a t midday or in the after-
noon. This phase of t8he rainfall has long been a subject for comment, even by comparative newcomers to this
area, but heretofore neither the exact facts nor their causes were known, and comment was based large,ly on
conjecture. Data have been compiled for the 20-year period, 1911-30, whic,h, it is believed, is of sufficient
length to a t least greably reduce any effects resulting from pronounced abnormalities. The data were tabulated
from the daily records of the local Weather Bureau office. These records contain not only the times of beginning and
ending of precipitation but also the hourly amounts, which were estracted from the 24-hour record sheets of a self- recording rain gage of the tipping bucket type. Eac.h
0.01 inch is registered on the sheets in the pr0pe.r hour division, but occasionally this unit amount mag be re-
corded in 1 hour yet be an accumulation of rain ext,ending over several hours; especially is this true of a drizzle or
cidedly greater frequency of rain d uring the late night
heavy mist. It is reasonable to believe, however, that
such cases are as numerous in any hour as another and that the relation of the total hours with a measurable amount,
or the total hourly amounts, is unaffected. In the first compilation the individual hours with 0.01
inch or more, by months, in the 20 years were counted. The sums obtained showed the trend of the hourly fre-
quency for each of the calendar months but the sums for
no month were strictly comparable with those of any other because of the variation in length of the months. To obviate this the sums were r0duce.d to a percentage
basis, shown in table 1, by dividing the total hours with a nieasurable quantity of rain by the total number of
hours. In the 31-day months the possible hours for each of the 24 were 620, in the months of 30 days there were 600, and in February, 5 of which were in leap years, the
divisor was 565. The annual hourly frequency percent- ages were found by dividing the number of rainy hours
of the same name in all monlhs by the possible 7,305 hours to obtain greater accuracy than the means of the
rnon thly hourly percentages would have given.