Review of Regional Weather and Smoke Haze for Jul 2014
1. Review of Regional Weather Conditions in July 2014
1.1 Southwest Monsoon conditions continued to prevail in July 2014 with low level winds over the region blowing mostly from the southeast or southwest. Rain bands from tropical cyclones during the first half of the month led to extensive rain clouds over most parts of the ASEAN region. However, the northward migration of the monsoon rain belt accompanied with an intensification of typhoon activities in the Western Pacific Ocean and South China Sea during the second half of the month brought dry weather conditions over the southern ASEAN region.
1.2 he western Pacific Ocean and northern South China Sea experienced 4 tropical cyclones in July 2014, namely Typhoon “Neoguri”, Typhoon “Rammasun”, Typhoon “Matmo” and Severe Tropical Storm “Nakri”. On 10 July 2014, Typhoon “Rammasun” developed to the southeast of the Mariana islands, tracked westwards and made landfall over Luzon island, the Philippines. “Rammasun” intensified as it entered into the South China Sea before making landfall over Hainan Island and moving across northern Vietnam on 18 and 19 July 2014 respectively. Typhoon “Rammasun” resulted in widespread damage, killing at least 200 people and injuring hundreds more.
1.3 During the month, many parts of the Mekong Sub-region received more than 125% of normal rainfall due to the presence of the monsoon rain belt in the northern hemisphere. In contrast, most parts of the southern ASEAN region received less than 100% of normal rainfall with the exception of central Sumatra and western Java where more than 125% of normal rainfall was received. The regional rainfall pattern for July 2014 is shown in Figure 1A.
Fig. 1A: Percentage of Normal Rainfall for July 2014. The rainfall data may be less representative for areas with low density of rainfall network.
2. Review of Land/Forest Fires and Smoke Haze Situation
2.1 The prevailing rainy season continued to help keep hotspot activities subdued in the northern ASEAN region. Few to scattered sporadic hotspots were detected mostly in Myanmar and Vietnam during brief periods of drier weather.
2.2 Wet weather conditions during the first half of the month helped to subdue hotspot activities in the southern ASEAN region. However, a period of drier weather conditions led to an increase in hotspot activities mainly over Borneo and the northern half of Sumatra during the second half of the month. Scattered hotspots with localized smoke plumes were detected over the northern half of Sumatra between 18 and 29 July 2014. During this period, some areas along the western coast of Peninsular Malaysia reported unhealthy levels of Air Pollutant Index (API) between 100 and 200. Port Klang had the highest API of 139 on 21 July 2014. Similarly, scattered hotspots with moderate smoke haze were also detected mainly in western Borneo. The smoke haze led to a drastic drop in air quality mainly in Sarawak with unhealthy readings recorded at Sibu, Samarahan and Sri Aman on 28 July 2014. The return of shower activities towards the end of the month helped to ease the smoke haze situation in the region. Satellite images depicting some of the hotspot activities over the ASEAN region in July 2014 are shown in Figs. 2A to 2E.
Fig. 2A: NOAA-18 satellite picture on 18 July 2014 showing slight to moderate haze from some of the hotspots in central Sumatra.
Fig. 2B: NOAA-18 satellite picture on 20 July 2014 showing smoke haze from Riau affecting parts of the Strait of Malacca and western Peninsular Malaysia.
Figure 2C: NOAA-18 satellite picture on 21 July 2014 showing moderate smoke haze over Riau spreading across the Strait of Malacca to affect the west coastal states of Peninsular Malaysia.
Fig. 2E: NOAA-18 satellite picture on 26 July 2014 showing moderate smoke haze emanating from hotspots in West Kalimantan.
Fig. 2D: NOAA-18 satellite picture on 24 July 2014 showing scattered hotspots with localised smoke haze over western Kalimantan .
2.3 The hotspot charts for July 2014 for
- Cambodia, Myanmar, Thailand, Lao PDR and Vietnam;
- Sumatra, Borneo and Peninsular Malaysia;
- Java, Sulawesi and the Philippines;
Fig. 2E: NOAA-18 satellite picture on 26 July 2014 showing moderate smoke haze emanating from hotspots in West Kalimantan.
Fig. 2F: Hotspot Counts in Cambodia, Lao PDR, Thailand, Vietnam, Myanmar for July 2014.
Fig 2G: Hotspot Counts in Java, Sulawesi, Philippines for July 2014.
3. Status of El Niño/La Niña
3.1 The tropical Pacific Ocean surface temperatures have continued to warm but gradually eased in recent weeks, slowing down the development of El Niño conditions. However, with most global climate models forecasting the continued warming of the tropical Pacific Ocean in the coming months, a weak to moderate El Niño is still likely to develop in the last quarter of 2014 .
3.2 Despite the observed warming over the tropical Pacific Ocean over the last few months, a number of atmospheric indicators of the El Niño, such as wind flow and cloudiness, have remained largely neutral. A plausible explanation for the lack of atmospheric response is that the warming has occurred over almost the entire tropical Pacific Ocean, including the sea areas in our region. During a typical El Niño development, warming is observed mostly in the eastern and central parts of the tropical Pacific Ocean.
3.3 In the last few months the sea surface temperatures in our region have been warmer than normal, leading to increased convection and formation of rain clouds. This has contributed to the relatively wet weather conditions in Singapore and the surrounding region during the current Southwest Monsoon season.
3.4 With the forecast of a weak to moderate El Nino in the last quarter of the year, it should be noted that the El Niño is known to have relatively less impact on weather patterns in Singapore and the nearby region during the Northeast Monsoon season (typically from late November to March). The risk of drier weather conditions due to the El Niño is thus expected to be lower towards the end of the year.
3.5 Typically the impact from El Niño for the Southeast Asia region is drier than average rainfall conditions, especially for the southern and eastern parts. More locally-specific impact differs from place to place and for different seasons. As the Southwest Monsoon season continues to prevail in the region, and with the possibility of a weak to moderate El Niño, the risks of occasional extended periods of drier and warmer conditions cannot yet be ruled out.