Only typhoons which passed within a 200-mile square box centered on the
islands of Rota and Guam and had wind speeds of 64 knots (typhoon strength) or
greater within the box were considered. From these typhoons, the following
considerations were applied to select a storm set for modeling. Tracks for the
selected typhoons are shown in Appendix A.
Strong and weak typhoon pairs. Typhoons typically approach Guam from
the east, continue moving toward the west past the island, and eventually curve
toward the northwest. A small number of typhoons have approached from the
south and continued moving northward past the island. Historical typhoons have
no evident preference for passing on one particular side of the island and occa-
sionally they pass directly across the island. A representative set of six strong
and weak typhoon pairs (12 storms) was selected for the following cases, based
on analysis of the types of tracks and storms:
a. West-moving, far north of islands.
b. West-moving, near north of islands.
c. West-moving, near south of islands.
d. West-moving, far south of islands.
e. North-moving, west of islands.
f.
North-moving, east of islands.
Typhoons passing near islands. All remaining typhoons which passed close
to the islands (basically between Guam and Rota or across either island) were
selected, a total of 14 storms. These storms are considered potentially damaging
because of their proximity to Guam.
Additional typhoons. The preceding criteria give a relatively complete and
representative set of historical storms affecting Guam. Several other typhoons,
not chosen initially by the criteria, were also reviewed to insure that all histori-
cally damaging storms were considered. These included three other candidate
strong storms for "west-moving, far north of islands," and a few other typhoons
on Rota and/or Apra Harbor. JTWC annual reports and storm reports were con-
sulted to see if any of these storms caused notable wave and flooding damage.
Based on these considerations, two additional typhoons were added to the model
set, giving a total of 28 storms.
Extreme typhoons. The impact of a typhoon on the study area at Apra
Harbor can be strongly affected by typhoon track. Historical data provide a
valuable record, but storms with small variations in the historical tracks would
have been equally likely. For analysis of extremes, it is important to capture
small variations in the most damaging storms which would have caused them to
be more damaging to the study area. These are referred to as hypothetical storms.
Two historical storms were considered with altered tracks to develop hypotheti-
cal cases to complete the storm data set: Paka (0597) and Olive (0163). Paka's
historical track past Guam was toward due west, just north of the northern tip of
7
Chapter 2
Storm Selection
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