If you want a good rain tire for our conditions in Portland, the last tire you want is an all-season tire. I know that this information does not help you, as you have already purchased the Bridgestone A/S tires, but it is a fact that cannot be repeated enough.
The National Highway and Traffic Safety Administration's (NHTSA) procedures for testing for Traction (wet braking) in its Uniform Tire Quality Grading (UTQG) suite of procedures are increasingly less relevant to modern vehicles. As you may confirm by plowing through the dense prose at the Code of Federal Regulations codification of the procedures (page 6 of 16 of the .pdf file), the tire under test is inflated to 24psi and mounted, with a load of 1,085 pounds, on a trailer that is then towed at 40 mph across a wetted surface. The wheel on which the tire is mounted then is instantaneously locked. The coefficient of friction of the locked tire then is measured not earlier than one-half (0.5) second after the wheel has been locked.
Most modern vehicles are equipped with antilock braking systems; I assume that your 2005 Sentra is so equipped. Feel free to correct me on the Sentra equipment. This is relevant to the UTQG rating system because it tends to mask the very weakness that all season tires exhibit.
The "all season" part of a tire's nomenclature refers to snow traction, not to rain traction. Now, it is tempting to think of rain as merely defective snow, and to assume that, if a tire has good traction in snow, then a fortiori (a fancy way of saying "even more so"), it must have good traction in the wet. In fact, exactly the opposite is true.
When a tire designer is finalizing the design of a tire, at some point he or she comes to a fork in the road where he or she has to decide if the tire's tread will be made with a rubber compound that is designed to shed as much water as possible so that the contact patch between the tread and the pavement is as nearly dry as possible, or whether the tread compound will be designed to stick to water (which is what snow becomes at the interface between the tire and the snow under the pressure of the mass of the vehicle) so that the tire will give snow traction. If the tread compound will be optimized to stick to snow, then, by the same action, water will adhere to the tread under rainy conditions. That water, a film between the tire's contact patch and the pavement, acts as a fairly good lubricant, compromising braking.
In the UTQG test procedure, the same small part of the tire's circumference that is the locked tire's contact patch is dragged across the pavement for a minimum of 29 feet (the distance traveled at 40mph in 0.5 seconds), which, eventually scrubs off the film of water that an all season tire will bring to the table. The measurement of the coefficient of friction does not even commence until the tire has been dragged at least 29 feet. However, on a vehicle equipped with an antilock braking system, the wheel will be rapidly unlocked and relocked many times in that 0.5 second, and therefore the ABS-equipped vehicle with all season tires will constantly present a fresh area of water-filmed tread to become the contact patch.
As noted above, like you, I live in Portland (in my case, actually in the city itself, but at an altitude of about 750 feet above downtown). At the end of April 2006, I purchased a new car that came with all season tires, and I drove them through the summer, under which conditions they were competent. But with the Portland winter rains approaching last October, I swapped the all season tires off the car and fitted three-season tires instead. In the few times I had driven the all season tires in the rain between April and October, I had experienced how loosey-goosey the all season tires were on wet pavement. The three-season tires I fitted in their place are orders of magnitude superior to the all season tires when the pavement is wet.
