CMDL Annual Report 24: 1.5.2 Samoa Climatology

1.5.2 Samoa Climatology

A comparison of SMOs 1996 and 1997 wind roses (Figure 1.6) to that of the 19-year period (Figure 1.7) shows a considerably higher percentage (69.8%) of clean air sector winds (north-northwest through southeast) in 1996 while 1997 (60.5%) was closer to the long-term average of 59.7%. The occurrence of winds in the 10 ms^-1 or greater class was 2.5% in 1996 and 5.0% in 1997 while the expected occurrence based on the 19-year average is 4.9%. The annual average wind speed for 1996 (4.7 ms^-1) was close to normal while 1997 (5.5 (ms^-1)(Table 1.11) was above normal.

Wind roses of surface winds for SMO for 1996 (left) and 1997 (right)

Fig. 1.6. Wind roses of surface winds for SMO for 1996 (left) and 1997 (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes.

Fig. 1.7. Wind rose of surface winds for SMO for 1977 through 1995. The distribution of resultant wind direction and speed are given in units of percent occurrence for the 19-year period. Wind speed is displayed as a function of direction in three wind classes.

TABLE 1.11. SMO 1996 and 1997 Monthly Climate Summary northeast of the main building

		Jan.	Feb.		March	April	May	June	July	Aug.	Sept.	Oct.	Nov.	Dec.	Year
									1996
Prevailing wind	NNW			NW	ESE	SE	SE	SE	SSE	SSE	SE	SSE	SSE	SE	SE
direction
Average wind	2.8		2.8		4.0	5.3	3.8	5.4	5.6	5.6	6.6	5.2	4.0	5.0	4.7
speed (m s^-1)
Maximum wind	8		13		14	11	13	11	10	11	14	12	10	12	14
*speed (m s^-1)**
Direction of max.	349		324		323	107	350	88	118	113	136	122	156	129	323
*wind (deg.)**
Average station	999.4		999.0		1000.2	1001.6	1002.4	1003.1	1003.0	1004.1	1002.2	1001.6	1000.6	998.9	1001.4
pressure (hPa)
Maximum pressure*	1005		1003		1008	1006	1007	1008	1007	1007	1006	1006	1005	1003	1008
(hPa)
Minimum pressure*	996		994		993	998	997	999	999	1001	998	997	996	994	993
(hPa)
Average air	27.9		27.6		27.6	27.5	27.3	27.2	27.1	26.1	26.1	26.1	27.1	26.9	27.0
temperature (°C)
Maximum temperature*	30		30		30	29	29	29	28	29	28	28	29	29	30
(°C)
Minimum temperature*	25		24		24	24	22	24	24	24	23	22	23	23	22
(°C)
Average dewpoint	24.2		25.2		25.7	24.4	24.2	24.8	23.7	21.6	22.8	23.8	24.9	24.5	24.2
temperature (°C)
Maximum dewpoint	26		27		28	26	26	26	26	25	26	26	27	26	28
temperature (°C)
Minimum dewpoint	22		23		23	22	21	22	21	16	19	21	21	22	16
Temperature (°C)
Precipitation (mm)	144		245		377	134	221	179	81	42	154	305	157	237	2277
									1997
Prevailing wind	E			SE	NNW	ESE	SSE	SSE	SSE	SSE	SSE	SSE	SSE	SE	SSE
Direction
Average wind	4.3		5.0		3.9	3.6	4.2	7.7	6.3	6.0	5.5	6.2	6.0	6.5	5.5
Speed (m s^-1)
Maximum wind	14		11		13	7	10	13	11	12	10	12	13	11	14
*Speed (m s^-1)**
Direction of max.	349		97		325	108	155	97	147	116	147	98	139	147	349
*Wind (deg.)**
Average station	999.6		999.7		998.9	1001.5	1001.4	1002.3	1002.6	1002.9	1003.7	1002.1	1002.6	999.4	1001.4
Pressure (hPa)
Maximum pressure*	1004		1004		1006	1006	1005	1006	1006	1007	1009	1006	1008	1004	1009
(hPa)
Minimum pressure*	992		996		989	997	997	993	999	998	998	998	998	993	989
(hPa)
Average air	26.3		26.9		26.4	26.9	26.2	25.7	25.9	25.5	26.0	26.5	26.6	26.9	26.3
Temperature (°C)
Maximum temperature*	29		29		28	29	29	27	28	28	29	29	29	29	29
(°C)
Minimum temperature*	23		23		24	24	23	24	23	23	23	24	24	25	23
(°C)
Average dewpoint	23.5		23.9		23.5	24.1	22.3	22.3	23.7	23.3	23.2	24.1	23.7	24.4	23.5
temperature (°C)
Maximum dewpoint	25		25		26	25	26	27	25	26	26	26	25	26	27
temperature (°C)
Minimum dewpoint	20		21		19	23	15	17	21	19	17	20	20	22	15
temperature (°C)
Precipitation (mm)	403		201		182	65	164	60	40	98	81	58	100	52	1503

Instrument heights: wind, 13.7 m; pressure, 78.5 m (MSL); air temperature, 14.0 m; dewpoint temperature, 12.8 m. Wind and temperature instruments are on Lauagae Ridge, 110 m northeast of the main building.

*Maximum and minimum values are hourly averages.

The average ambient temperature for 1996 (27.0°C) was close to the to 19-year average of 27.1°C while 1997 (26.3°C) was cooler than normal. The average barometric pressures for 1996 and 1997 (Table 1.11) were both 2.1 hPa above the 19-year average of 999.3 hPa. New high-pressure records were set during the months of March 1996, June 1996, September 1997, and November 1997. High-pressure records were tied during the months of January 1996 and May 1996. June 1997 set a new record low pressure for the month. The amount of precipitation in 1996 (2277 mm) was wetter than normal while 1997 (1503 mm) was considerably drier than normal.

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