Weather & Tides.
Generally the weather in tropical regions is difficult to predict. Around the equator there is a constant area of low pressure (around 1010 mbar) with only slight daily fluctuations, resulting in frequent calms. The winds are thermic in origin due to differences in temperature over sea and over land. A normal wind pattern shows a relatively calm morning with a sea breeze developing in the afternoon, sometimes up to 15 knots. In the evening and at night a land breeze can occur.
The weather pattern around Singapore is characterized by two dominant monsoon seasons. The NE monsoon, roughly from December to March, and the SW monsoon, from April till September. In between these distinct monsoon periods are the transitional periods with generally very light winds. The NE monsoon has generally slightly stronger winds than the SW monsoon, but the wind is hardly more than 10 to 15 knots, sometimes piping up for a few days till in the mid twenty range.  During periods of a prolonged NE monsoon wind the seas east of Malaysia can be quite rough with waves up to 5 meter and many times warnings are given out for small vessels. In de SW monsoon the Straits of Malacca can be quite choppy, but generally the waters there are more protected (by Sumatra), except in the north, near Langkawi and Phuket, where the sea can be quite rough due to the much stronger winds there and the swell coming in from the Indian Ocean. But the area is great for sailing.

The Straits of Malacca  is known for its many thunderstorms during which winds can be quite gusty; 30 knots or more is not an exception. Quite nasty are the 'Sumatras' (also called Westerlies) from about April to October. They are quite heavy thunderstorms, developing over land (Sumatra) and finding its way to the east. The wind can be as strong as 50 to 60  knots and the sea can get quite rough. Fortunately they do not last long (30 minutes to an hour) and the moment the rain starts pouring down the worst is actually over. After the storm the sea is back to normal very soon. Be careful if you sail at night as in a dark night these storms can easily get unobserved till they are there. It is good practice to constantly keep an eye on the sky as thunderstorms develop very fast. If the wind drops completely and you feel a drop in temperature, your better reef immediately.

In the Malacca Straits  there is constantly lightning most nights, which does not necessarily mean that a thunderstorm is approaching. It can be a beautiful and peaceful passage

Your barometer does not warn for the heavy winds that come with a thunderstorm. Generally the barometer pressure in the area is around 1010 mbar. It fluctuates daily with a minimum of about 1006 mbar in the afternoon.

Singapore weather forecast:

Local newspapers. Information provided is very basic. No information about wind direction and/or strength unless the winds are expected to be very strong

http://weather.msn.com/  general weather forecast for various regions, including satellite images

http://weather.yahoo.com/_sv=off   general weather forecast for various regions

http://www.weather.gov.sg/wip/web/home/further_outlook   for short and long term forecast.

WINDGURU provides wind direction and strength including wave height and rainfall for the east coast area for 7 days ahead:

http://www.windguru.cz/int/index.php?sc=312 

UNDERGROUND website provides weather for Singapore, including wind speed and direction:

http://www.wunderground.com/cgi-bin/findweather/getForecast?query=singapore

Regional weather forecast: 

WINDGURU provides wind direction and strength including wave height and rainfall for various areas for 7 days ahead:

http://www.windguru.cz/int/index.php  wind directions over more days with wind shifts and wave directions

UNDERGROUND website provides weather for many parts of Singapore and Thailand, including wind speed and direction: 

http://www.wunderground.com/global/MS.html

The Singapore National Environment Agency (NEA) provides weather information in general, including a specific shipping weather forecast for the regional waters

http://www.weather.gov.sg/wip/c/portal/layout?p_l_id=PUB.1023.7   

weather forecast including tropical storm warnings for Phuket, Malacca, Tioman, Condore, Bunguran and Reef 

The Malaysian Meteorological Office has a website that provides info about wind speed, direction, temperature and precipitation and also wave height, including maritime warnings:

http://www.kjc.gov.my/english/weather/forecast/ship.html  

The Thai government also provides weather info that is easily accessible via the web:

http://www.tmd.go.th/en/ weather forecast for Thailand, including more days forecast, storm warnings, weather maps, weather radars, satellite images and wave heights

Via NAVTEX:

The region has the following Navtex stations: 

Navtex stations: Singapore ( C ) ; Malaysia (S, T, U); Thailand F: Indonesia (A, B, D, E): Vietnam (W, P, X); Hong Kong (L)

Worldwide:

http://www.oceanweather.com/about/index.html  ocean weather world wide, including actual wave height, wave direction, wind direction etc as well as forecasting

Tides.

The tidal range in the regional waters is around 2 meter. Tidal streams (currents) are in the 1 knot range, except in a few areas around spring tide, where tidal currents up to 3  knots can occur. This is in Singapore waters: east of Changi Naval base, around Tekong and on the way into Serangoon Harbour. Also in the Straits the current can be strong and there are many eddies. Eddies and overfalls are also common in the Buran Channel (south of Sentosa, especially in the western part. These overfalls are made worse by the sometime heavy ferry traffic that enters the channel at high speed. For small boats it can be a dangerous area.

In the Straits of Malacca the current can be quite strong as well, specially near the entrance (Kukup) and in between Malacca and Port Klang. Also at One Phatom Bank (NW of Port Klang) the current can be up to 3 knots and it is wise to plans the trip along this stretch of water to make use of the current instead of fighting it. If you sail north (or south) and go inside the Klang River, beware of strong currents as well.

In the eastern part of the Singapore Straits near Horsburgh Lighthouse, currents are strong and the sea is many times very confused, especially with wind against current. Also the stretch of water between Batam and Bintan has strong currents

Tidal information for Singapore (Tanjong Pagar) is published daily in the newspaper and can also be obtained via mobile phone (see under weather) Singapore tide tables are available at Motion Smith

Motion Smith:
76 Shenton Way #01-01
Singapore 079119
Tel : (65) 6220 5098
Fax : (65) 6225 4902
Email: sales@motsmith.com
http://www.motsmith.com

Also the United Kingdom Hydrographic Office (UKHO) has a website from which one can download tidal information from all over the world for a period of 7 days ahead:

http://easytide.ukho.gov.uk/EasyTide/EasyTide/index.aspx

For Singapore (Tanjung Pagar) the website is: http://easytide.ukho.gov.uk/EasyTide/EasyTide/ShowPrediction.aspx?PortID=4718&PredictionLength=7

Please note that there are slight differences in the time and level of high/low water at various Singapore sites. For a more precise prediction use proper time tables (Admiralty) with primary and secondary ports, available at Motion Smith