Here is a great website for weather in Malaysia. Click on the specific destination. On the destination page you will find something called "trip planner" - add your dates and it will give you the best indication of what to expect.
I have only been to Malaysia( Penang) in April so can't help I'm afraid.

Hi Fiona,

Thanks for your reply. I have looked at this site you have recommended but there is no data held for Langkawi for the dates I have selected.

Thanks again

that's a shame. We have some recommended weblinks here where you can get a fair bit of info.

I have stayed on the East Coast of Malaysia in June and August. The weather when we visited was a mixture of sunshine and the occasional heavy tropical downpour. We stayed at the Swiss Garden Resort which was fine but not really a honeymoon style hotel (Not if you have been considering the Pangkor Laut Resort). We also visited the Hyatt Regency in Kuantan, fine four star type property.There is a hotel owned by the same company who own the Pangkor Laut on the east coast - The Tanjong Jara resort...never been so can't comment but it is a luxury property. Same group also owns the Ritz-Carlton in KL.

We also stayed for three nights in Taman Negara, but that was in February. We saw some rain then it should be better in July. But you are right in the rainforest so fair chance of some rain.

Have not been to Pangkor Laut, but have stayed on the nearby island of Pangkor. (They're a couple of mile apart). Stayed in Feb so can't comment on the weather for the July period.