The island where it never rains...

[corsita]

Hello Community,

I noticed that the island we live on has most of the time an almost rain free area around itself.

In this example, looking at the last hour this rain free area remained in the display, even though it was pouring outside. If you look at this last hour you can see the red area approchaing Koh Mak. But when it arrives, Koh Mak stays light blue (even though it is pouring outside)

I started the web version with another username and browser and did not allow windy to locate me (since I thought that maybe it is doing that around my location). But no. Still have this rain free area.

Is there some logical explanation to this?

Our location N11°49'4",E102°29'27"

[Korina]

@corsita Hello, do you have any radar source for comparison?

[Gkikas LGPZ]

@corsita
Weather models show rain in this location.

I think you are reffering to radar imagery.

As your location is far away from radar site, maybe you are located
in an area within radar "shadow zone".

Source: https://www.radartutorial.eu/07.waves/wa01.en.html

[dodohjk]

@corsita
WIndy is taking the data directly from the thai met serivce.
https://www.tmd.go.th/en/ and https://weather.tmd.go.th/

They have a number of rain radar stations. Navigating through i think there are two that cover the island of Ko Mak

The further away Suvarnbhumi which could have some mountains in the way.
https://weather.tmd.go.th/svp240.php

and the closer one is Sattahip https://weather.tmd.go.th/satLoop.php

which appears to be in a direct line of sight, thus i would not expect any radar shadow to affect the island.

I am not sure why Ko Mak appears to be without rain. However, i don't think you can trust the rain radar for the area in general. This is the edge of the range of the rain radar and the quality of the data deteriorates the further out you go. Mainly is due to problems with detecting a good signal bouncing back and in particular with the radar beam being very high above the ground.
The beam is at a shallow angle upwards (probably 2° or 3°), but in 200km range that is 7-10km; Any rain below that is not going to be detected

[corsita]

@dodohjk Thank you for the extensive explanation.

I meanwhile "discovered" two more areas that behave the same.

I do not see any logic in why this would be like that.

I did realize we are at the edge of the range (I actually always tought it would be satellite data). But the data we see here is very accurate. When I can see rain (dark red clouds) coming it matches what Windy is showing. Just when the rain area reaches that shadow, it disappears in Windy but not in reality.

Will probably remain a mistery.

Concerning the line of sight to Sattahip: I do not know the exact radar position but I suppose it is on a 148 meter hill south of Sattahip. Mountains in the near area are not in the way. But it actually means the radar is looking (due to earth curvature) at an altitude of aproximately 3000 meter (9850 feets) over our island. That makes me wonder about how the data is collected. The dark red rainy clouds are definetly lower than 3000 meters.

[Korina]

@corsita Hello, if the radar source shows this kind of data, we are not able to affect it or change it.

[Bruzote]

Seeing as you didn't get a complete answer, you could contact the Thai Met service. You might get an answer. If you don't, it's no harm to you. Ask them if they know why this happens. You might no answer, a clear answer, or varying levels of speculation about different possible reasons.