If you're planning on taking a vacation this summer, here or abroad, I have some advice for you: Do not procrastinate. 

Here's why.

1. More are flying

Not so long ago a lot of folks put vacation plans on hold, thanks to 2008's recession. Here are some passenger traffic snapshots of those days (domestic and international) for the month of August, courtesy of the Bureau of Transportation Statistics.

--2008: 67.7 million passengers

--2009: 65.0 million passengers

Now look at last year's numbers.  

--2014: 69.3 million passengers

Even more people will fly in 2015.  Thanks to a perfect storm of strong dollar and continuing cheap fuel prices and an economy on the upswing, airline seats will be at a premium.

2. Flights will be packed

In the past few years, airlines have turned capacity-cutting into an art form; they know how many want to fly and how many seats they need to hold us all. Since more passengers are expected to fly this summer, the airlines have pricing power on their side. When demand is up, prices are too.

3. Watch for limited summer deals

You may not be aware of this but since late December, Southwest Airlines sales have mostly been limited to flights on Tuesdays, Wednesday and Saturdays (prior to this, sales were good on flights any day except Friday or Sunday). Southwest isn't alone, either. JetBlue deals have long been limited to Tuesday and Wednesdays only and others have similar sale restrictions. Bottom line: Fewer days for sale flights means fewer seats at the cheapest possible prices which is another sign that the time to start planning a summer vacation is now.

4. Shop for summer now

Most of the current crop of airfare sales are valid only for flights through June 3 or so. After that, watch prices jump (and jump again in late June) as more and more people vie for an increasingly small number of deals and seats. The airlines know that most of us wait to make plans within 30 days of departure, and price their fares accordingly meaning tickets will be more expensive.

The sooner you move - particularly if you're going to Europe - the better your chance of getting the flight you want at the price you want, or at least coming close to a good deal. If you procrastinate, you may not get a seat on the flight you want at all.

Rick Seaney is an airline travel expert and the co-founder of FareCompare.com, an airfare comparison shopping site