252 seamanship secrets
Do we have enough time to make port or should we move farther off shore to
gain sea room?
You can make a simple weather pattern log to organize the information
you need to make decisions (see illustration). Use your horizontal rows for
your hourly observations, setting up blocks for 3-hour intervals. Set up vertical
columns for Temperature, Barometer, Pressure Change, Wind (direction and
speed), Cloud Type, Cloud Cover (%), Waves, and Visibility. You can add
a large comments space at the end of each 3-hour interval. Below are some
guidelines for filling out your log.
WEATHER PATTERN LOG SUBJECT FIELDS
Te m p e r a t u r e. Note whether temperature is rising, steady, or falling.
Barometer. Observe the barometric pressure trend over the 3-hour period.
Record the direction and speed of movement as follows: steady, rising slowly
or rapidly, or falling slowly or rapidly. Note a pressure rise or fall of more than
1 millibar (0.03 inch) during the 3-hour period. Remember that in an area of
signifi cant diurnal variations, as discussed earlier, the readings at 0400 and 1600
hours will be slightly lower than baseline, and those at 1000 and 2200 hours will
be slightly above baseline.
Winds. Estimate the direction and average speed over the previous
3 hours and record those details as follows: backing (shifting counterclock-
wise); veering (shifting clockwise); steady; increasing; decreasing.
A synoptic chart of the northern Pacifi c Ocean: the tightly spaced isobars to the west of the
961 mb low-pressure system indicate winds that will be stronger than those that precede
the passage of the front.