Al Dykes said:

I live in an area where three zones meet on the zone map.
It seems to me that instead of guessing my effective zone, planting
tomatoes comes down to soil temperature and the expected minimum
nighttime temperature.

I go by night time low temperatures, based on historical weather data and
the trending each year. You can plant tomatoes when the expected lows
will be 50 degrees F or better. According to weather.com, for Staten Island
that will be May 9. Wait a couple of more days and you would likely have
no risk of frost at all. (I've had frost on clear, windless nights where the
offficial measured low was about 34 degrees.)

Staten Island, May historic data (watch line wrap):

http://www.weather.com/outlook/homea...USNY1401?climo
Month=5
--
Pat in Plymouth MI ('someplace.net' is comcast)

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)