AGROCLIMATIC INFORMATION FOR AGRICULTURAL PLANNING AND OPERATION IN ILOCOS NORTE PARTICULARLY BATAC AND SURROUNDING AREAS FOR THE MONTH OF AUGUST

I. AGROCLIMATIC SUMMARY::

Cloudy to overcast skies with scattered to occasional rains is the normal weather in the area. Total rainfall amount averages 504.6 mm with 18 rainy days. An extreme 24-hr total rainfall amount of 326.0 mm was recorded on August 29, 1990. The longest wet spell of 14 days was also recorded on August 16-19, 1985 (941.8 mm). The highest total monthly rainfall amount usually falls in the month of August. Normal total evaporation of 127.8 mm are the normal values for the month.

Soil moisture is generally wet. Humid environment prevails with average relative humidity of 85%. Drying condition is poor. Leaf wetness duration is from 6 to 12 hours. Daylight duration is 12 hours and 50 minutes with 36% total bright sunshine. This situation gives an amount of 17.8 MJ/m2 of solar radiation during most days of the month. Southerly to southeasterly winds prevail.

Average maximum air temperature is 31.8 °C with an extreme of 36.5°C as what was recorded on August 13, 1987. Meanwhile, average minimum air temperature is 23.9°C with an extreme coolness of 17.8°C as what was recorded on August 4, 1977.

II. AGROCLIMATIC DATA (AVERAGE)::

Decade Rainfall Rainy P(W)* P(TC)** Tot AIR TEMPERATURE RH Solar Wind
(10 Day) (mm) days % % evap. Max. Min. (%) Rad. Speed
          (mm) (°C) (°C)   MJ/m2 (kpd)
August                    
1-10 128.3 6 75 24 42.2 32.0 24.0 84 17.6 47.3
11-20 166.0 6 79 52 40.2 31.7 24.0 85 17.9 42.5
21-31 310.3 6 79 43 45.4 31.8 23.9 85 18.0 47.7

Ten-day rainfall depth at different probability levels for August in Batac, Ilocos Norte

Decade Mean Rainfall Probable rainfall depth
    25% 50%
1-10 128.3 138.5 21.2
11-20 166.0 168.7 23.3
21-31 310.3 212.4 16.3
TOTAL 504.6 519.6 60.8

* Probability of wet decade (>50 mm per decade)

** Probability of having a Tropical Cyclone

Initial probabilities that a given decade is dry (D) or wet (W) and transitional probabilities that one, two or three days within a decade is dry or wet.

August Initial
(%)
Transitional %
D W DD WD DW WW DDD WDD DWD DDW WWD WDW DWW WWW
1-10 25 75 17 83 29 71 0 0 5 4 12 22 16 42
11-20 21 79 0 100 22 78 0 0 4 0 11 8 17 51
21-31 21 79 50 50 18 82 6 5 4 8 15 7 11 44
DD -- probability of a dry day given that the previous day was dry
DW -- probability of a dry day given that the previous day was wet
WD -- probability of a wet day given that the previous day was dry
WW -- probability of a wet day given that the previous day was wet
DDD -- probability that three consecutive days are dry
WWW -- probability that three consecutive days are wet
WWD -- probability that two consecutive days are wet and the third day is dry
WDW -- probability that within three days the second day is dry

III. TROPICAL CYCLONE

Historical records shows that Northern Luzon is within the Normal Tropical Cyclone Track. The following tropical disturbances that crossed or passed closed over Ilocos Norte from 1981-2006.

TC Name Year and Date Occurrence
TS Openg Aug 17, 1981
T Norming Aug 24-26, 1982
TD Goring Aug 14-15, 1984
TD Huaning Aug 16, 1984
TS Maring Aug 27-30, 1984
T Ibiang Aug 19, 1985
TS Luming Aug 26, 1985
T Ising Aug 17, 1987
T Gading Aug 15-19, 1990
TS Heling Aug 24-27, 1990
T Iliang Aug 29-30, 1990
TD Luding Aug 11-13, 1991
TS Isang Aug 27-30, 1992
TS Huling Aug 26-30, 1993
TD Pasing Aug 01-03, 1994
T Ritang Aug 04-07, 1994
T Susang Aug 17-20, 1994
TD Diding Aug 07-10, 1995
TS Etang Aug 21-23, 1995
T Gening Aug 25-31, 1995
TD Isang Aug 03-04, 1996
TS Lusing Aug 18-21, 1996
TD Daling Aug 01-10, 1997
TD Ibiang Aug 1997
TS Miling Aug 22-29, 1997
TS Bising Aug 01-04, 1998
TD Klaring Aug 07-09, 1998
TS Luding Aug 18-21, 1999
T Isang Aug 20-22, 2000
TS Lusing Aug 27-28, 2000
TD Jolina Aug 16, 2001
TS Juaning Aug 01-04, 2003
TD Lakay Aug 18-19, 2003
T Niña Aug 20-24, 2003
T Onyok Aug 29-Sept 03, 2003
T Marce Aug 22-27, 2004
T Chaba Aug 28, 2004
TS Gorio Aug 02-04, 2005
TS Huaning Aug 11-13, 2005
T Isang Aug 30-31, 2005
TD Inday Aug 06-07, 2006

RAINFALL DEPTH AT DIFFERENT PROBABILITIES OF OCCURRENCE FOR AUGUST 1-31

DATE RAINFALL DEPTH (mm)
25% 50%
1 6.4 0.4
2 11.4 1.6
3 17.6 3.4
4 14.2 5.0
5 23.6 3.8
6 10.6 1.8
7 12.4 1.2
8 10.9 1.2
9 19.8 1.0
10 11.6 1.8
11 10.0 0.4
12 16.8 0.4
13 11.5 0.7
14 17.4 1.5
15 18.6 2.6
16 27.2 7.4
17 16.6 5.1
18 24.0 4.0
19 10.0 0.8
20 16.6 0.8
21 10.2 0.8
22 17.8 3.6
23 27.0 4.0
24 15.2 0.8
25 28.0 1.6
26 30.0 4.3
27 10.4 0.8
28 12.4 0
29 44.0 0.4
30 14.4 0
31 3.0 0

DAILY RAINFALL PROBABILITY (GRAPH)