Predicting Mersing weather?

[Canopus Lim]

I have been following the satellite images. Basically the satellite images taken that are posted on NEA are about 3h behind...so it cannot tell current situtation. Secondly, through analysis of the photos, the satellite images only shows clouds that are going to rain (water droplets big). Because it is IR pictures, IR has poorer penetration through larger water droplets (Mie Scattering) and hence only thick, dark clouds will be displayed in the Satellite images.

For high altitude clouds or clouds that are thin, it will not be reflected on the satellite images as these clouds have smaller water droplets and IR light can penetrate it better. Therefore, even though the Singapore forecast is 'fair'..it can be horrible skies because of high altitude clouds and not because of thick clouds that are going to rain.

I can tell reasonably well if Mersing skies have useable skies based on Singapore's weather. Why do I say so? As said earlier, I find it a rule of thumb that if Singapore can see some stars, Mersing skies will fare much better. When there are great Singapore skies, Mersing skies will be the best. There are many reports of great Mersing skies and that all correlated with Singapore having fantastic skies. When there are some stars seen in Singapore, Mersing skies will tend to be useable. How useable cannot be defined because the clouds keep moving and are high dynamic. However, if the sky in Singapore is extremely bad that not even one bright star nor the moon can be seen and that continues for hours or days in the role, Mersing skies in general will be bad. Therefore for the extreme conditions (very clear and very bad), Singapore skies can reflect what is seen at Mersing.

Last year I have been to Mersing and 4 days I have experienced extremely bad conditions even for many hours (days in fact)..not even a single star can be seen. When back in Singapore ,it is the same situation. The reason is due to a massive big rain cloud kind that covers the entire penisular Malaysia. The satellite images can help to ascertain whether it is very bad condition. For example the timing gave by Gavin is that at mid night it became very cloudy in Mersing, true. The massive cloud took 2h to travel to Singapore and I experienced that cloud at 2am and observed it coming from the north and through the satellite images. I would think the big cloud later cleared and maybe a few hours later Singapore was 'clear' again and Mersing would have been clear at the time Gavin has stated when he observed the second time hours later from 12 midnight.

Therefore not to sound so negative, I am just stating that Mersing skies can be very good to very bad. Also, basing on Singapore skies, one can reasonably predict if the sky will be useable or fantastic in Mersing. Therefore, to summarize, if Singapore's skies days before have the trend of seeing some stars or many stars, Mersing skies in general will be useable.

[rcj]

A note about the weather images. NEA is currently using the Japanese satellite based on the MTSAT-1R which was launched in 2005. There is a newer one already in orbit called the MTSAT-2 which is the next generation version. Both consists of 5 bands of study, including two IR channels. MTSAT-2 provides greater bit depth and resolution which NEA has not implemented as yet. In any case, the frequency of images downloaded from the satellite sensor is once per 20 minutes on a daily basis, 24 hours a day. If you need this frequency, you will have to write in and most probably incur high cost. Used to work on this project, and the conclusional basis, we are interested to analysis a parameter called TBB (Temperature Black Body) from the IR channels. Low values indicate the presence of high clouds. In convective regions like our tropics, this is an important study as high clouds indicate deep convective cycles which is strongly correlated to a high rainfall area or the potential for heavy precipitation. However, what NEA show on the page is for users to "just see" if there are clouds, and not always the actual scientific data. Nevertheless my point to make is that satellite images show a plethora of information. Whether it is used in useful ways or meaningful analysis is another. In short, it is good to know what the presence of high clouds mean in this example.

[starfinder]

A note about the weather images.

Wow, take that from a satellite image specialist!

With regards to the satellite images which we see on the NEA website, do they show all the clouds which are there? Canopus Lim thinks it does not: "satellite images only shows clouds that are going to rain (water droplets big). Because it is IR pictures, IR has poorer penetration through larger water droplets (Mie Scattering) and hence only thick, dark clouds will be displayed in the Satellite images. "

I notice that there are several kinds of satellite images displayed on the NEA website: http://app.nea.gov.sg/cms/htdocs/catego ... asp?cid=59

For example, the MTSAT Asean IR images as displayed for the consumer show the least amount of clouds, whilst the FY2-C and NOAA images show a lot more clouds. See for comparison:
http://app.nea.gov.sg/cms/htdocs/article.asp?pid=1454
http://www.weather.gov.sg/wip/web/ASMC/ ... Asia/FY2-C


Also, what's your experience with the Telok Sari obs site weather, its predictability, variability, and also connection with Singapore's cloud cover? Do you think there are essential differences in weather patterns and visibility/transparency there versus Singapore? Wah, many questions!

(As an aside, I have a theory/suspicion that the large Tioman island at NE 30km offshore with its tall peaks do have an effect on the Telok Sari cloud cover situation, since the winds and clouds seem to arrive at Telok Sari from the E and NE. Perhaps it traps or diverts some of the clouds? Hmmmm... Wild guess).

[Canopus Lim]

Hi Gavin,

I base it on Latest ASEAN-modified MSTAT satellite images. The resolution of it is also pretty bad since it cannot even resolved singapore on the map. Small clouds smaller than the size of Singapore will not be displayed too.

I come to the conclusion that it only display rainfall or thick clouds because whenever the weather forecast state it is fair.... and the satellite images also show 'no cloud', one still see high altitude clouds in Singapore. Therefore it does not represent every cloud in the sky. Perhaps it just show a wavelength band in IR and thus does not represent every cloud? If it shows all the information.. think the satellite image will be in a mess and no trained person will be able to know what it represents.

Also the update rate is quite slow since it is Free..actually I stated it wrongly as it is not 3h.. but probably 1h behind as I got mixed up with the Nowcast. Well.. if it is 1h, it is still not updating fast enough as within half an hour the whole sky in Singapore can be clouded up and I have experienced such clouding up many times unfortunately when I am setting up my scope...

So.. probably the best way to predict Mersing's sky is based on a combination of weather reports, number of stars seen in Singapore day before or days before trip, trend in the weather (whether having afternoon shower and night time clear trend) and satellite images. Lastly.. a bit of luck on the side of the person going there.

I have tried my luck quite many times when there is massive overcast covering the entire peninsular Malaysia and Singapore as I thought that Mersing skies were 'magical' (being not related to Singapore sky at all)...and I paid the price of mosquito bites..wasted trip..wasted effort .. money and time for perhaps 7 Mersing nights. Last trip to Tioman island 1 month back...was the same.. crappy Singapore skies for consequtive days.. in Tioman the same crappy skies (Tioman should have more magic since it has even darker skies than Mersing). I expected crappy skies so I just brought binoculars on that trip only. I guess I have wised up a bit.

[starfinder]

Tks Yang Beng, Remus and Chee Chien (other thread) for your commentary on Mersing's weather and satellite imagery. It's very interesting stuff!


Yang Beng, did you spend 4 and 7 consecutive nights at the Telok Sari observing site? Sounds like a lot! Surely not alone? Yikes! I suppose you stayed in a hotel in Mersing town or at Sari Mawar chalet during the day. About 5 years ago, I stayed during the day at Timotel hotel in town in-between two night's observation at Telok Sari. Was there with Remus and we saw Albert Lim and TASOS people there too.


Anyway, my rough estimate of my own experiences at Telok Sari out of the 15 or so trips I've been there since around 1999/2000 is probably as follows:

A. Nights where it was totally cloudy and I saw next to nothing - 10%

B. Nights where it was mostly cloudy and only some small patches were clear for brief periods - 10%

C. Nights where it was mostly cloudy but several patches were clear for prolonged periods - 20%

D. Nights where it was 1/2 cloudy and 1/2 clear [edit] during the night, i.e. evenly mixed - 30%

E. Nights where it was 3/4 clear 3/4 of the time - 20%

F. Nights where it was mostly clear throughout the night - 10%

G. Nights where it was totally clear throughout the night - 0%.


The above is a rough estimate only from memory, as I've not kept track of it. I would say that:

A & B (20% total) would certainly not have been worth the trip, if star gazing was the sole objective, but the beachside walk, company, and ride up is nice anyway. A good escape from urban Singapore. Plus KFC there is cheaper and fresher.

C maybe worth it star-gazing wise if the clear patches were in good areas.

D, E, F, and G would be considered a success. That adds up to about 60% of the time.

G I've not experienced, though maybe one night was close. I have heard of such nights from Remus about 3 years ago. Alas I was not there.

I would say that this past Sat's trip there was under D.

When a night is under C & D (total 50%), its best to stay longer to increase chances of success.


Of couse, A-G describe cloud cover. In addition, there is the factor of general seeing conditions, moisture, etc, which can affect the views through a scope.

Rain-wise, I've experienced moderate to heavy rain at Telok Sari perhaps about 15% of the time.

[ADD: apart from 1 or 2 trips in Nov and Dec, my trips were made during the months of Feb-Oct, since the Monsoon period is around Nov-Jan].


In terms of co-relation to weather in Singapore. Hmmm... tough one. I think if there is a very large-scale cloud system over Peninsular Malaysia and the South China Sea, then yes, both areas would be cloudy at the same time for several days. Otherwise, I'm not so sure. Didn't really keep track. Overall, I think Telok Sari's weather and cloud cover and Singapore's tend to be different. I would say that Telok Sari tends to be less cloudy than Singapore, perhaps only slightly. Plus I think there is a quality to the skies there when it's clear that is special.

Apart from the co-relation, there is the main element which is the variability at Telok Sari itself within one night, just like last Saturday's.


Anybody would like to share their experiences, esp under the A-G classification above? We could do a poll! Pls state no. of times you've been to Telok Sari as a baseline.

[acc]

A. Nights where it was totally cloudy and I saw next to nothing - 5% (twice)

B. Nights where it was mostly cloudy and only some small patches were clear for brief periods - 5%

C. Nights where it was mostly cloudy but several patches were clear for prolonged periods - 30%

D. Nights where it was 1/2 cloudy and 1/2 clear [edit] during the night, i.e. evenly mixed - 30%

E. Nights where it was 3/4 clear 3/4 of the time - 20%

F. Nights where it was mostly clear throughout the night - 5%

G. Nights where it was totally clear throughout the night - 5%.

Well the above are my very approx estimates. I have been to Mersing about 30 times.

Basically I could only recall two occasions when I came back empty-handed err empty-eyed At least one-quarter of the time its raining on the way there (sometimes cats and dogs). There have been occasions when it rained in Mersing town or Singapore, but the sky was clear in the ob area. (heck, there were even times when its rainy in Tampines but clear at tiong bahru). And as Gavin pointed out, there were many nights when it went from completely overcast to clear (and vice-versa) within one hour. So that's why I never bother to predict the weather lor

[Canopus Lim]

Wow.. 5 to 10% wasted trips only. I guess you guys ought to follow me more often to increase this percentage. Just joking. Anyway, if you want to experience bad Mersing weather, one ought to go now... these few days the rain has come in (it always happens after a dry and hot spell) and Peninsular Malaysia and Singapore is completely overcast. The chance of having a good night at Mersing is extremely low.

I don't have too much opportunities to go to Mersing as I am usually busy on the weekends but I do observe locally often. I observe most of the time when ever the clouds clear and probably setup my scope about 20x a year or more. From what I observe, Singapore's weather is such that it rains continuously for many days..and there will be a break on average 2 to 3 days of good skies..and continue to rain again for few or many days. If one were to go to Mersing during these period of rain, the chance of meeting bad skies is much higher than during the period of good skies in Singapore.

For example the recent Mersing trip, I could not make it due to personal things but actually wanted to go. I guessed the skies would be useable due to what I have observed in Singapore (dry weather, quite clear skies in Singapore at night, day time with open clouds.. no overcast). And it turned out true and that is not the only time. It occurs many times. From the trip reports to Mersing, I would say all of them tallies what is expected..that means those useable trips occur during periods when Singapore skies have stopped raining (I refer to big rains that last whole day, overcast conditions)..that window of few days with clear (or useable) skies. These useable days tend to have showers in the afternoon and clear skies in the evening. Maybe I am obsessed but I observe the weather everyday since I am on standby everyday to bring out my scope.

My last trip to Tioman..though not for stargazing, is the same (2 nights crappy skies). There was a storm going on and Singapore was raining cats and dogs for many days continuously and at night the sky is so bad that not even a star is seen. With this kind of adverse weather, even Tioman or Mersing will not escape. This can be seen in the satellite chart where the massive cloud, as large as Peninsular Malaysia hovers there for days..or weeks. Therefore, for such situation, it is best not to take risk to go Mersing as the probability is very low... in my case 0 percent success.

Perhaps my posts sounds rather negative but is not meant to be. What I have stated is to describe my experience with bad Mersing skies so that people can perhaps make a better decision on when to go. I would go to Mersing whenever I have the chance since Mersing skies is the best there is near us, but this time round I will check the weather signs to mitigate the risk of wasted trips.

[weixing]

Hi,
Base on my few Mersing experience, good clear sky in Mersing usually start with bad or not so good weather when on the way to Mersing... Anyway, I think I had better luck... most of the trips I went was actually range from very good to quite good. I think only had one trip of total bad sky in Mersing... it's become a lightning show.

So my conclusion is similar to acc that the weather in Mersing can be quite difficult to predict... it's may be very clear in the day, then bad at early evening and suddenly clear up again after mid-night or it's may be very bad in the day, but very clear at night. So just pray hard and keep all your fingers and toes crossed.

(heck, there were even times when its rainy in Tampines but clear at tiong bahru).

By the way, talk about weird weather, I had experience quite a number of time in Singapore that one way of the road is very dry, but the other way is raining quite heavily... ha ha ha

Have a nice day.