Report :

Thunderstorm Characteristic Event at Seberang Jaya, Penang

Prepared by:

DISASTER RESEARCH NEXUS

SCHOOL OF CIVIL ENGINEERING

UNIVERSITI SAINS MALAYSIA

Characteristic of Thunderstorm in Malaysia

1.0 Introduction

Malaysia are located near the equaotorial belt. The wind system in this country is dominated by two monsoon periods, namely the northeast (NE) monsoon season from December to March and southwest monsoon (SW) season from June to September. On the other hand, there are frequent occurrences of tropical thunderstorm (TS), especially during inter-monsoon periods between April–May and October–November. The winds produced by TS events are relatively stronger and more turbulent than those produced by monsoon winds. Therefore, TS winds are important and need to be understand since it can cause damage especialy to building structure.

Every thunderstorm is produced by a cumulonimbus cloud and is always accompanied by lightning and thunder. A thunderstorm usually lasts no more than 1 hours and it begins when a parcel of air, either warmer than the surrounding or being pushed up by colder encroaching air such as a cold front, begins to rise. This unstable up-draught forms the embryo of the thunderstorm. If the rising air is sufficiently moist, condensation will occur to form cloud droplets. A large amount of moisture condenses and precipitation particles begin to grow as the cell continues to build up.

Figure 1 : Schematic diagram showing downdraught during thunderstorm (Choi, 1999)

Table 1.1 : Thunderstorm categories

Category Wind Speed Precipitation

Ordinary < 18m/s (40 mph) VariableApproachingSevere

≥18m/s (40 mph) Hail > ½ inch

Severe ≥26m/s (58 mph) Hail ≥ ¾ inch

1.1 Location

In this field study, Telekom Malaysia Communication Tower in Seberang Jaya, Penang has been chosen as a meteorological station. This meteorological station is provided by IRPA Grant and it is used for the purpose of data observation for the research. The operation of data collection of this meteorological station was begun from 1 st. of April 2002. The data that have been used in this research is for two years period which begin from January 2003 and ended by December 2004 where there were approximately 18720 data has been collected

Instrumentation consist two parts which is the first part is the Ultra sonic Wind Sensors WAS425 to determine the wind speed, temperature, relative humidity, pressure and wind direction. The Ultra sonic Wind Sensors WAS425 has been mounted on Telekom Malaysia Communication Tower 3 different levels of height of this tower. The levels are :-

i. Level A – 45.72mii. Level B – 75.28m

iii. Level C – 97.23m

The type of data that have been produce by anemometer is short period record where it is able to detect wind speed, relative humidity, pressure, temperature and wind direction within 30 minutes interval. Figure 3 shows the WAS425 Ultrasonic wind sensor which has been used in this research. Figure 4 shows schematic diagram of WAS425 Ultrasonic wind sensor position at Telekom Malaysia Communication Tower in Seberang Jaya.

Figure 3 : Ultrasonic Anemometer Sensor

Level A Level B Level C46 m 75 m 97 m

Figure 4 : Schematic diagram of ultrasonic anemometer sensor position at Telekom Malaysia Communication Tower in Seberang Jaya, Penang

1.2 Results

Throughout the 2 years period of data year 2003 -2004, there are more than 60 thunderstorm events have been identified. But, there are only three thunderstorm events have been highlighted in this research where the value of wind speed is more than 17.9m/s or 40mph. The thunderstorm event which have been identified were occurred at :-

i. 5.30 p.m on 11 April 2003ii. 10.30 a.m on 29 July 2004

iii. 12.30 p.m on 15 August 2004

In this study, there are 5 parameters have been discussed in order to determine thecharacteristic of thunderstorm during thunderstorm event such as wind speed, temperature, relative humidity, pressure and wind direction.

2.0 Thunderstorm Event at 5.30 p.m on 11 April 2003

i. Wind speed

The first thunderstorm event occurred at 17.30 on 11 April 2003. Figure 4.2 shows the time series plot graph of wind speed for wind A and wind B. From the graphs (Figure 2.1) it indicates that there are a huge increases in wind velocity between during thunderstorm event and non- thunderstorm event. For example, the velocity of wind A at 16.00 is 3.2 m/s , at 16.30 is 2.3m/s and at 17.00 is 2.8m/s which are the increases is about 506.3%, 743.5% and 592.9% respectively. During thunderstorm event at 17.30, the wind speed was increase dramatically from 2.8m/s to 19.4m/s where the increase is about 592.9%. After thunderstorm event, which is at 18.00 the wind speed tends to decrease. From the graph (Figure 4.2), the wind speed shows the rapid drop from 19.4m/s to 7.7m/s which is the decreases is about 60.3%. Then, it tends to decrease moderately at 18.30 and 19.00 which the value of wind speed are 3.3m/s and 1.7m/s respectively.

Whereas for wind C, the increases of wind speed value also rose up dramatically. From the graph, it indicates that there is the increases in wind speed value where the value of wind speed at 17.00 is 2m/s but during the thunderstorm event at 17.30, the wind speed rose up dramatically from 2m/s to 22.1 m/s where it contribute about 1005% increases. After the thunderstorm event, the wind speed value tends to decrease rapidly from 22.1 m/s to 8.4m/s and this decreases is about 172.9%. The trend of wind speed after thunderstorm event tends to decrease moderately where the value of wind speed at 18.30 and 19.00 is about 4.4m/s and 2.1 m/s respectively. Figure 4.2 shows times series plot of wind speed at 17.30 on 11 April 2003. Table 2.1 shows the value of wind speed for wind A, wind B and percentage wind speed changes at 17.30 on 11 April 2003.

Figure 2.1 : Time series plot of wind speed at 17.30 on 11 April 2003.

Table 2.1 : Value of wind speed for wind A, wind B and percentage wind speed changes at

17.30 on 11 April 2003.

Time

Wind% Wind Speed

Changes

A B Wind A Wind B

16.00 3.2 4.2 506.3 426.2

16.30 2.3 3.4 743.5 550.0

17.00 2.8 2 592.9 1005.0

17.30 19.4 22.1TS

EVENTTS

EVENT

18.00 7.7 8.4 60.3 -172.9

18.30 3.3 4.4 83.0 -275.5

19.00 1.7 2.1 91.2 -312.8

ii. Temperature

Figure 2.2 shows the time series plot graph of temperature for temperature A and temperature B. From the graph, it shows that the decreases in temperature value where the temperature value before thunderstorm event is higher than temperature value during thunderstorm event. At 17.00, the temperature is 29.5oC and during thunderstorm event the temperature went lower to 28oC which cause decreases of 51%. For temperature B, it also shows the same trend where temperature value during thunderstorm event is slightly lower than before thunderstorm event. During thunderstorm event at 17.30, the temperature is 28oC and before thunderstorm event at 18.00 the temperature is 29.5oC. The temperature value after thunderstorm event is tend to decrease moderately where the temperature at18.00, 18.30 and 19.00 is 25.7oC , 26oC, and 26oC respectively. This decrease is about 7.1% to 8.1 %. Figure 4.3 shows times series plot of temperature at 17.30 on 11 April 2003. Table 2.2 shows the value of temperature for temperature A, temperature B and percentage of temperature changes at 17.30 on 11 April 2003.

Figure 2.2 : Time series plot of temperature at 17.30 on 11 April 2003

Table 2.2 : Value of temperature for temperature A, temperature B and percentage

temperature changes at 7.30 on 11 April 2003.

Time Temperature

% Temperature Changes

A BA B

16.00 31 30.6 -9.7 -8.5

16.30 29.9 29.5 -6.4 -5.1

17.00 29.5 29.1 -5.1 -3.8

17.30 28 28TS

EVENTTS

EVENT

18.00 25.3 25.7 9.6 8.2

18.30 24.1 26 13.9 7.1

19.00 24.4 26 12.9 7.1

iii. Relative Humidity

Figure 4.4 shows the time series plot graph of relative humidity for relative humidity A and relative humidity B. The graph shows that the relative humidity value during thunderstorm event is higher than before thunderstorm event. During thunderstorm event at 17.30, the relative humidity value is 90 % and before thunderstorm event which is at 16.00, 16.30 and 17.00 is 67%, 75% and 82% respectively. After thunderstorm event, the relative humidity value tends to increase moderately from 90% to 91%. The same trend applies to relative humidity B where the relative humidity value during thunderstorm event is higher than before thunderstorm event. After thunderstorm event, the relative humidity value tends to increase the relative humidity value rose up from 90% to 91%. Figure 2.3 shows times series plot of relative humidity at 17.30 on 11 April 2003. Table 2.3 shows the value of relative humidity for relative humidity A, relative humidity B and percentage of relative humidity changes at 17.30 on 11 April 2003.

Figure 2.3 : Time series plot of relative humidity at 17.30 on 11 April 2003

Table 2.3 : Value of relative humidity for relative humidity A, relative humidity B and

percentage of relative humidity changes at 7.30 on 11 April 2003.

Time

Relative Humidity % R. Humidity Changes

A B A B

16.00 67 68 34.3 32.4

16.30 75 75 20.0 20.0

17.00 82 81 9.8 11.1

17.30 90 90 TS EVENT TS EVENT

18.00 91 91 -1.1 -1.1

18.30 91 91 -1.1 -1.1

19.00 91 91 -1.1 -1.1

iv. Pressure

Figure 2.4 shows the time series plot graph of air pressure. The graph shows that the pressure value during thunderstorm event is lower than after thunderstorm event. During thunderstorm event at 17.30, the pressure value is 1008.8hPa and after thunderstorm event which is at 18.00, 18.30 and 19.00 is 1009.3 hPa, 1009.3hPa and 1009.3 hPa respectively. Before thunderstorm event, the pressure value tends to decrease moderately from 1008.2hPa to 1007.8hPa. Figure 2.4 shows times series plot of pressure at 17.30 on 11 April 2003. Table 4.3 shows the value pressure and percentage of pressure changes at 17.30 on 11 April 2003.

Figure 2.4 : Time series plot of pressure at 17.30 on 11 April 2003

Table 2.4 : Value of pressure and percentage of pressure changes at 7.30 on 11 April 2003.

Time Pressure

% Pressure

Changes

16.00 1008.2 0.06

16.30 1007.7 0.11

17.00 1007.8 0.10

17.30 1008.8TS

EVENT

18.00 1009.3 -0.05

18.30 1009.3 -0.05

19.00 1009.3 -0.05

v. Wind Direction

Figure 2.5 shows the time series plot graph of wind direction. The graph shows that the wind direction value during thunderstorm event is fluctuating where for direction A , the wind direction moves from 22o to 57o and direction B from 26o to 82o From the graph, it indicates there is a sudden changes in wind direction during thunderstorm event. Figure 2.5 shows times series plot of wind direction at 17.30 on 11 April 2003. Table 2.5 shows the value wind direction and percentage of wind direction changes at 17.30 on 11 April 2003

Figure 2.5 : Time series plot of wind direction at 17.30 on 11 April 2003

Table 2.5 : Value of wind direction and percentage of wind direction changes

at 7.30 on 11 April 2003.

Time Wind Direction

% Wind Direction Changes

A BA B

16.00 30 31 90.0 100.0

16.30 61 59 -6.6 5.1

17.00 22 26 159.1 138.5

17.30 57 62TS

EVENTTS

EVENT

18.00 45 46 21.1 25.8

18.30 48 45 15.8 27.4

19.00 38 37 33.3 40.3

3.0 Thunderstorm Event on 10.30 a.m on 29 July 2004

i. Wind SpeedThe second thunderstorm event occurred at 10.30 on 29 July 2004. Figure 2.6

shows the time series plot graph of wind speed for wind A and wind C. From the graphs (Figure 3.1) it indicates that there are a huge increases in wind velocity between during thunderstorm event and non- thunderstorm event. The velocity of wind A at 9.00 is 3.2 m/s , at 9.30 is 3.5m/s and at 10.00 is 5m/s which are the increases is about 231.3%, 202.9% and 112.0% respectively. During thunderstorm event at 10.30, the wind speed was increase dramatically from 5.0m/s to 10.6m/s where the increase is about 112%. After thunderstorm event, which is at 11.00 the wind speed tends to decrease. From the graph (Figure 3.1), the wind speed shows the rapid drop from 10.6m/s to 1.2m/s at12.00 which is the decreases is about 88.7%. Then, it tends to decrease moderately at 11.30 and 12.00 which the value of wind speed is 4.1m/s and 1.2m/s respectively.

For wind C, it also shows the same trend where wind speed value during thunderstorm event also rose up dramatically. From the graph, it indicates that there is the increases in wind speed value where the value of wind speed at 10.00 is 6.1m/s but during the thunderstorm event at 10.30, the wind speed rose up dramatically from 6.1m/s to 19.3 m/s where it contribute about 216.4% increases. After the thunderstorm event, the wind speed value tends to decrease rapidly from 19.3m/s to 2.1m/s at 12.00 and this decreases is about 88.6%. The trend of wind speed after thunderstorm event tends to decrease moderately where the value of wind speed at 11.30 and 12.00 is about 5m/s and 2.2 m/s respectively. Figure 3.1 shows times

series plot of wind speed at 10.30 a.m on 29 July 2004. Table 2.6 shows the value of wind speed for wind A, wind B and percentage wind speed changes at 10.30 a.m on 29 July 2004.

Figure 3.1 : Time series plot of wind speed at 10.30 a.m on 29 July 2004.

Table 3.1 : Value of wind speed and percentage of wind speed changes at 10.30 a.m on 29 July 2004..

Time

Wind% Wind Speed

Changes

A C Wind A Wind C

9.00 3.2 3.8 231.3 407.9

9.30 3.5 6 202.9 221.7

10.00 5 6.1 112.0 216.4

10.30 10.6 19.3TS

EVENTTS

EVENT

11.00 9.5 12.7 -10.4 -34.2

11.30 4.1 5 -61.3 -74.1

12.00 1.2 2.2 -88.7 -88.6

ii. Temperature

Figure 3.2 shows the time series plot graph of temperature for temperature A and temperature C. From the graph, it shows that the increases in temperature value where the temperature value before thunderstorm event is lower than temperature value during thunderstorm event. At 10.00, the temperature is 26.4oC and during thunderstorm event the temperature went lower to 26.7oC which cause increases of 1.1%. For temperature C, it also shows the same trend where temperature value during thunderstorm event is slightly higher than before thunderstorm event. During thunderstorm event at 10.30, the temperature is 25.9oC and before thunderstorm event at 10.30 the temperature is 26.2oC. The temperature value after thunderstorm event is tend to decrease moderately where the temperature at11.00, 11.30 and 12.00 is 26.2oC , 23.9oC, and 25.5oC respectively. This decrease is about 2.7% to 8..81 %. Figure 4.8 shows times series plot of temperature at 10.30 on 29 July 2004. Table 4.7 shows the value of temperature for temperature A, temperature C and percentage of temperature changes at 10.30 on 29 July 2004.

Figure 3.2 : Time series plot of temperature at 10.30 a.m on 29 July 2004.

Table 3.2 : Value of temperature and percentage of temperature changes at 10.30 a.m on 29 July 2004.

Time Temperature

% Temperature Changes

A CA C

9.00 24.4 24.7 9.4 6.1

9.30 25.3 25 5.5 4.8

10.00 26.4 25.9 1.1 1.2

10.30 26.7 26.2TS

EVENTTS

EVENT

11.00 26.7 26.2 0.0 0.0

11.30 24.1 23.9 -9.7 -8.8

12.00 26.1 25.5 -2.2 -2.7

iii. Relative Humidity

Figure 3.3 shows the time series plot graph of relative humidity for relative humidity A and relative humidity C. The graph shows that the relative humidity value during thunderstorm event is lower than before thunderstorm event. For relative humidity A, during thunderstorm event at 10.30, the relative humidity value is 81 % and before thunderstorm event which is at 9.00, 9.30 and 10.00 is 84%, 84% and 83% respectively. After thunderstorm event, the relative humidity value tends to increase moderately from 77% to 84%. The same trend applies to relative humidity B where the relative humidity value during thunderstorm event is lower than before thunderstorm event. After thunderstorm event, the relative humidity value tends to increase where the relative humidity value rose up from 77% to 86%. Figure 2.8 shows times series plot of relative humidity at 10.30 a.m on 29 July 2004. Table 3.3 shows the value of relative humidity for relative humidity A, relative humidity B and percentage of relative humidity changes at 10.30 a.m on 29 July 2004.

Figure 3.3 : Time series plot of relative humidity at 10.30 a.m on 29 July 2004.

Table 3.3 : Value of relative humidity and percentage of relative humidity changes at 10.30 a.m on 29 July 2004

Time

Relative Humidity% R. Humidity

Changes

A C A C

9.00 84 85 -3.6 -2.4

9.30 84 85 -3.6 -2.4

10.00 83 84 -2.4 -1.2

10.30 81 83TS

EVENTTS

EVENT

11.00 84 86 3.7 3.6

11.30 84 86 3.7 3.6

12.00 77 77 -4.9 -7.2

iv. Pressure

Figure 3.4 shows the time series plot graph of air pressure. The graph shows that the pressure value during thunderstorm event is lower than after thunderstorm event. During thunderstorm event at 17.30, the pressure value is 1008.8hPa and after thunderstorm event which is at 18.00, 18.30 and 19.00 is 1009.3 hPa, 1009.3hPa and 1009.3 hPa respectively. Before thunderstorm event, the pressure value tends to decrease moderately from 1008.2hPa to 1007.8hPa. Figure 3.4 shows times series plot of pressure at 10.30 a.m on 29 July 2004.. Table 2.9 shows the value pressure and percentage of pressure changes at 10.30 a.m on 29 July 2004.

Figure 3.4 : Time series plot of pressure at 10.30 a.m on 29 July 2004.

Table 3.4 : Value of relative humidity and percentage of relative humidity changes at 10.30 a.m on 29 July 2004.

Time Pressure

% Pressure

Changes

9.00 1011.2 0.15

9.30 1011.7 0.10

10.00 1011.8 0.09

10.30 1012.7TS

EVENT

11.00 1012.8 0.01

11.30 1012.8 0.01

12.00 1012.6 -0.01

v. Wind Direction

Figure 3.5 shows the time series plot graph of wind direction for wind direction A and C. The graph shows that the wind direction value during thunderstorm event is fluctuating where for direction A , the wind direction moves from 50o to 42o and direction C from 53o to 38o. after thunderstorm event, the wind direction moves again from 42o to 37o and direction C from 38o to 37o. From the graph, it indicates there is a sudden changes in wind direction during thunderstorm event. Figure 3.5 shows times series plot of wind direction at 10.30 a.m on 29 July 2004. Table 2.10 shows the value wind direction and percentage of wind direction changes at 10.30 a.m on 29 July 2004.

Figure 3.5 : Times series plot of wind direction at 10.30 a.m on 29 July 2004.

Table 3.5 : Value wind direction and percentage of wind direction changes at 10.30 a.m on

29 July 2004.

Time Wind Direction

% Wind Direction Changes

A CA C

9.00 59 57 -28.8 -33.3

9.30 57 53 -26.3 -28.3

10.00 50 53 -16.0 -28.3

10.30 42 38TS

EVENTTS

EVENT

11.00 37 37 -11.9 -2.6

11.30 33 34 -21.4 -10.5

12.00 38 35 -9.5 -7.9

4.0 Thunderstorm Event at 12.30 p.m on 15 August 2004

i. Wind Speed

The third thunderstorm event occurred at 12.30 p.m on 15 August 2004. Figure 3.1 shows the time series plot graph of wind speed for wind A and wind C. From the graphs (Figure 4.1) it indicates that there are a huge increases in wind velocity between during thunderstorm event and non- thunderstorm event. The velocity of wind A at 11.00 is 2.3 m/s , at 11.30 is 2.7m/s and at 12.00 is 6.5m/s which are the increases is about 804.3%, 607.4% and 220.0% respectively. During thunderstorm event at 12.30, the wind speed was increase dramatically from 6.5m/s to 20.8m/s where the increase is about 220%. After thunderstorm event, which is at 13.00 the wind speed tends to decrease. From the graph (Figure 4.1), the wind speed shows the rapid drop from 20.8m/s to 6.7m/s at 13.00 which is the decreases is about 67.8%. Then, it tends to decrease moderately at 13.30 and 14.00 which the value of wind speed are 3.2m/s and 2.0m/s respectively.

For wind C, it also shows the same trend where wind speed value during thunderstorm event also rose up dramatically. From the graph, it indicates that there is the increases in wind speed value where the value of wind speed at 12.00 is 7.2m/s but during the thunderstorm event at 12.30, the wind speed rose up dramatically from 7.2m/s to 25.1 m/s where it contribute about 248.6% increases. After the thunderstorm event, the wind speed value tends to decrease rapidly from 25.1m/s to 7.4m/s at 13.00 and this decreases is about 70.5%. The trend of wind speed after thunderstorm event tends to decrease moderately where the value of wind speed at 13.30 and 14.00 is about 3.8m/s and 3.2 m/s respectively. Figure 4.1 shows times series plot of wind speed at 12.30 p.m on 15 August 2004. Table 4.1 shows the value of wind speed for wind A, wind C and percentage wind speed changes at 12.30 p.m on 15 August 2004.

Figure 4.1 : Times series plot of wind speed at 12.30 p.m on 15 August 2004.

Table 4.1 : Value of wind speed for wind A, wind C and percentage wind speed changes at 12.30 p.m on 15 August 2004.

Time

Wind% Wind Speed

Changes

A C Wind A Wind C

11.00 2.3 2 804.3 1155.0

11.30 2.7 2.5 670.4 904.0

12.00 6.5 7.2 220.0 248.6

12.30 20.8 25.1TS

EVENTTS

EVENT

13.00 6.7 7.4 -67.8 -70.5

13.30 3.2 3.8 -84.6 -84.9

14.00 2 3.2 -90.4 -87.3

ii. Temperature

Figure 4.2 shows the time series plot graph of temperature for temperature A and temperature C. From the graph, it shows that the increases in temperature value where the temperature value before thunderstorm event is lower than temperature value during thunderstorm event. At 11.00, the temperature is 29.0oC and during thunderstorm event the temperature rose up to 29.6oC which cause increases of 2.0%. For temperature C, it also shows the same trend where temperature value during thunderstorm event is slightly higher than before thunderstorm event. During thunderstorm event at 12.30, the temperature is 28.9oC and before thunderstorm event at 11.00 the temperature is 28.1oC. The temperature value after thunderstorm event is tend to decrease moderately where the temperature at13.00, 13.30 and 14.00 is 28.9oC , 25.2oC, and 24.6oC respectively. This decrease is about 12.8% to 14.9 %. Figure 4.13 shows times series plot of temperature at 12.30 p.m on 15 August 2004. Table 4.2 shows the value of temperature for temperature A, temperature C and percentage of temperature changes at 12.30 p.m on 15 August 2004.

Figure 4.2 : Times series plot of temperature at 12.30 p.m on 15 August 2004.

Table 4.2 : Value of temperature for temperature A, temperature C and percentage of temperature changes at 12.30 p.m on 15 August 2004.

Time Temperature

% Temperature Changes

A CA C

11.00 29 28.1 0.0 2.8

11.30 29.2 28.7 -0.7 0.7

12.00 29.6 28.9 -2.0 0.0

12.30 29.6 28.9TS

EVENTTS

EVENT

13.00 29.6 28.9 0.0 0.0

13.30 26.1 25.2 -11.8 -12.8

14.00 24.9 24.6 -15.9 -14.9

iii. Relative Humidity

Figure 4.3 shows the time series plot graph of relative humidity for relative humidity A and relative humidity C. The graph shows that the relative humidity value during thunderstorm event is lower than before thunderstorm event. For relative humidity A, during thunderstorm event at 12.30, the relative humidity value is 69 % and before thunderstorm event which is at 11.00, 11.30 and 12.00 is 73%, 71% and 67% respectively. After thunderstorm event, the relative humidity value tends to increase moderately from 69% to 86%. The same trend applies to relative humidity B where the relative humidity value during thunderstorm event is lower than before thunderstorm event. After thunderstorm event, the relative humidity value tends to increase where the relative humidity value rose up from 70% to 86%. Figure 4.3 shows times series plot of relative humidity at 12.30 p.m on 15 August 2004. Table 4.3 shows the value of relative humidity for relative humidity A, relative humidity B and percentage of relative humidity changes at 12.30 p.m on 15 August 2004.

Figure 4.3 : Times series plot of relative humidity at 12.30 p.m on 15 August 2004.

Table 4.3 : Value of relative humidity for relative humidity A, relative humidity B and percentage of relative humidity changes at 12.30 p.m on 15 August 2004.

Time

Relative Humidity% R. Humidity

Changes

A C A C

11.00 73 75 -5.5 -6.7

11.30 71 73 -2.8 -4.1

12.00 67 70 3.0 0.0

12.30 69 70TS

EVENTTS

EVENT

13.00 86 86 24.6 -22.9

13.30 86 86 24.6 -18.6

14.00 86 84 24.6 -16.3

iv. Pressure

Figure 4.4 shows the time series plot graph of air pressure. The graph shows that the pressure value during thunderstorm event is lower than after thunderstorm event. During thunderstorm event at 12.30, the pressure value is 1011.6hPa and after thunderstorm event which is at 13.00, 13.30 and 14.00 is 1012.2 hPa, 1012.2hPa and 1010 hPa respectively. Before thunderstorm event, the pressure values remain constantly at 1010.9hPa. Figure 4.4 shows times series plot of pressure at 12.30 p.m on 15 August 2004. Table 4.4 shows the value pressure and percentage of pressure changes at 12.30 p.m on 15 August 2004

Figure 4.4 : Times series plot of pressure at 12.30 p.m on 15 August 2004.

Table 4.4 : Value pressure and percentage of pressure changes at 12.30 p.m on 15 August 2004.

Time Pressure

% Pressure

Changes

11.00 1010.9 0.07

11.30 1010.9 0.13

12.00 1010.9 0.13

12.30 1011.6TS

EVENT

13.00 1012.2 0.06

13.30 1012.2 0.06

14.00 1010 -0.16

v. Wind Direction

Figure 4.5 shows the time series plot graph of wind direction for wind direction A and C. The graph shows that the wind direction value during thunderstorm event is fluctuating where for direction A , the wind direction moves from 49o to 48o and direction C from 48o to 47o. After thunderstorm event, the wind direction moves again from 48o to 47o and direction C from 47o to 45o. From the graph, it indicates there is a sudden changes in wind direction during thunderstorm event. Figure 4.5 shows times series plot of wind direction at 12.30 p.m on 15 August 2004 . Table 4.5 shows the value wind direction and percentage of wind direction changes at 12.30 p.m on 15 August 2004.

Figure 4.5 : Times series plot of wind direction at 12.30 p.m on 15 August 2004 .

5.0 Conclusion

During thunderstorm event, it indicates that there is a sudden and huge increases in wind speed value and after thunderstorm event there is a rapid drop in wind speed value. This value are very important especially for deisgn building structure. The temperature and pressure during thunderstorm event having a rapid drop where the temperature and pressure will decrease dramatically. During thunderstorm event also, the relative humidity will increase and there is a sudden change in wind direction.

Thus, all these characteristic of thunderstorm is similar with the characteristic of thunderstorm which discovered from previous study.