Let's approach the issue of dry, wet and damp runway conditions from the pavement engineering perspective. Dry runway means that the dry weather friction can be expected (which is usually good). Damp runway means that the wet weather friction can be expected (which can range from fair to poor; it is not usually poor and would only be so on greasy or polished stone surfaces which are very rare on runways). Wet runway means that the wet weather friction can be expected plus there can be standing water (friction can range from fair to very poor; it can easily be poor or very poor because standing water can lead to aquaplaning).
Now the normal runway micro surface (that is the surface seen from very close-up) should be a little bit rough, just as it should be on any road. ICAO requires a minimum texture for a new surface of 1mm. In fact, as I tell my students of pavement engineering, if you fall off your bicycle, you should skin your knee. This means that the surface has some texture. The texture enables the stones imbedded in the surface to stick up above any water, and small rain showers or very thin sheets of standing water can dissipate between the stones as the tyre rolls over them, and this ensures that no aquaplaning occurs unless there is lots of standing water.
Most [black coloured] runways are surfaced with asphalt (asphaltic concrete for the Americans and bituminous concrete for the British). This typically has a very smooth surface, and the ungrooved texture is low/poor. I measured a pretty smooth asphalt surfaced carpark the other day to test a new texture measuring machine, and got 0.4mm. Normal asphalt texture varies but an average could be 0.6mm. If you fall off your bicycle, you won't skin your knee. Small rain showers or very thin sheets of standing water cannot dissipate between the stones because the surface is so smooth that it doesn't have any stones sticking up. Asphalt needs grooving.
The few runways that are "sealed" or "chip sealed" are also black and have a rough texture (typically 1.5mm) and you will skin your knee if you fall off your bicycle. Sometimes the airport will put a chip seal (aka surface dressing) on top of the asphalt to get the same effect.
Grooving is an artificial way of restoring texture to asphalt, and it is a Good Thing. It gives the gaps that the water can dissipate into as the tyre rolls over the asphalt. A grooved runway is restored to being equivalent in surface texture to a surface that is a little bit rough. The ICAO groove spacings of 3mm x 3mm @ 25mm centres adds 0.4mm to the asphalt texture of say 0.6mm, which gives 1.0mm. The "big tropical" grooves of 6mm x 6mm @ 31mm centres add 1.1mm texture, giving typically 1.1+0.6=1.7mm. An asphalt runway that is not grooved is a) a lot cheaper to build, and b) plain dangerous. You'll sometimes see a few around the place, disappearing rapidly under your wing as you frantically try and stop in the wet. The other treatment you may see, which is equivalent in terms of restoring texture to grooving, is "porous", and it is also a Good Thing.
For example, look at Perth, Australia - the 06/24 and 03/21 runways are respectively porous and grooved (well done Torb). This simply means that they are now up to normal surfacing standards in terms of texture. Look at Cairns, Australia - the 12/30 and 15/33 runways are respectively sealed and grooved. This means that 12/30 is already at normal texture surfacing standards, and 15/33 is up to normal surfacing standards (well done Andy).
Grooving won't cope with standing water due to ruts and birdbaths in the runway (common in worn-out runways). Grooving won't cope with deep standing water due to heavy rainstorms (hint: equatorial). Grooving won't cope with standing water due to all the grooves and texture being filled up with rubber (hint: Bangkok).
If you can see standing water (puddles or sheets of water glistening) as you line up, then you should be concerned regardless of whether the book says the runway has been grooved or not.
In conclusion, grooved asphalt should be treated as a normal runway surface, and normal limits applied (wet/dry etc) without further regard to whether it is grooved or not. Ungrooved asphalt or "not porous" asphalt should be considered as sub-standard and treated with caution. By the way, the groves give no grip at all in themselves, and I cannot see why any crosswind limitations should be changed on grooved runways.
[This message has been edited by OverRun (edited 10 April 2001).]