Monthly Weather Bulletin

MOnthly weather bulletin

JULY 2007

1. SUMMARY

In general, the country received average to very much above average amounts of rainfall. In most places, the temperatures recorded were higher than the long-term average value. The country recorded lower than average amounts of daily solar radiation and experienced lower rates of evaporation.

2. RAINFALL

July falls in the peak of the Southwest Monsoon. During this month, heavy rains are noted in several areas in Peninsular Malaysia. The total amount of rainfall is recorded as average to much above average. This was due to the higher than normal sea surface temperature at the East of Indian Ocean and the less frequency of tropical storms activities over the Pacific Ocean and northern South China Sea. Thus, the southwesterlies flows that usually carries dry weather in Peninsular Malaysia becomes weak and it caused the development of convective cloud clusters in afternoon and early night which as a result, brings about an increase in rainfall in this month. Other than that, the elongated monsoon troughs which are normally formed at the northern South China Sea to the western Pacific Ocean were found unstable during July. This caused the southwesterlies flows become weak and allowed trade wind to penetrate into this region. The convergence between southwesterly and easterly wind had contributed to increase the formation of cloud clusters and causing heavy rains with thunderstorms to occur in the evening over Peninsular Malaysia.

Sabah and Sarawak received very much above average rainfall. Moisture brought by the easterly wind from the Pacific Ocean, strong vertical shear and the unstable atmosphere condition had enhanced the formation of cloud clusters in East Malaysia. These occurrences had caused heavy rains towards this region along the month.

As for total monthly rainfall, Pulau Langkawi recorded the highest total rainfall of 389.5 mm where as Temerloh recorded the lowest total rainfall of 81.6 mm. Over East Malaysia, Tawau recorded the highest total rainfall of 495.2 mm while Kudat recorded the lowest total rainfall of 154.6 mm.

Based on the classification scheme, there were 3 stations recorded very much above average rainfall, 18 stations recorded above average and 12 stations recorded average rainfall. It was noted that Prai, KLIA station and Tawau recorded the highest rainfall on record for the month of July with 296.2 mm, 258.0 mm and 495.2 mm respectively. The number of rain days for Peninsular Malaysia varied from 12 to 24 days while the East Malaysia recorded 14 to 21 days.

3. TEMPERATURE

Generally, most places in the country had higher than average temperature. The mean temperature of the month over lowland areas varied from 26.1°C to 27.7°C as recorded at Senai and Kota Bharu respectively. Mersing recorded the largest positive deviation of +0.8°C from normal.

The mean minimum temperature over lowland areas varied from 22.8°C (Kuala Terengganu Climate Station) and 25.0°C (Labuan). The lowest temperature of the month was 21.5°C being recorded at Ipoh, Subang and Petaling Jaya.

The mean maximum temperature over lowland areas varied from 30.2°C (Tawau) to 33.0°C (Temerloh). The highest temperature registered in the month was 35.6°C, in Kota Kinabalu.

Cameron Highlands, a highland station, had temperature ranging from 14.4°C to 26.3°C with a mean temperature of 18.1°C.

4. SOLAR RADIATION

The country generally received below average amount of solar radiation. The daily mean values varied from 10.73MJm-2 at Senai to 19.56MJm-2 at Miri. The largest positive and negative deviations from normal were +2.87MJm-2 and -3.78MJm-2 at Miri and Senai respectively.

5. EVAPORATION

In line with low solar radiation, the country experienced lower rates of evaporation during this July. The daily mean evaporation rate over the lowland areas ranged from 2.4mm/day (Kluang) to 4.4mm/day (Sibu). The largest negative deviation was
-0.8mm/day (Kota Bharu) while the largest positive deviation was +0.6mm/day (Chuping).

The mean daily evaporation rate at Cameron Highlands was 1.8mm/day, with the deviation of -0.2mm/day.
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Figures and tables:

Figure 1 : Rainfall Map for Peninsular Malaysia
Figure 2 : Rainfall Map for Sabah and Sarawak