twenty knots in the regions between Eniwetok and Wake.
Small amounts
of cumulus cloud, usually about 5/10 coverage, are found in this cur.
rent.
They do not extend much above 8,000 feet in the north or
12,000 feet in the south.
in sometimes falls from some of these
clouds, particularly in the south, but it is usually in the form of
light showers.
No extensive middle or upper cloud decks are found,
Although the lower winds are northeasterly and quite fresh, as one
ascends in the atmosphere over the northern Marshalls one finds that
the-winds turn more westerly with increasing elevation until at
about 20,000 feet they lie between northwest and southwest.
The
westerlies then extend upwards to the tropopause, increasing in
speed to about thirty-five knots at 45,000 feet; above the tropopause the winds again become easterly.
If the tropospheric upper
winds in the region should be mainly southwesterly, rain from the
trade cumulus is likely and the amount of cloud may increase from
time to time to as much as 8/10.
On the other hand, if these up~
per winds are chiefly northwesterly in direction, cumulus clouds
may decrease to as little as 2/10 or 3/10 and showers are less
likely.
The variation between northwest and southwest is controlled
by an upper level pressure trough which tends to be located just
west of Eniwetok during trade weather.
The difficulties in fore~
casting variations in trade weather, then, are associated with small
movements of the trough line to and from across the northern Mar~
shalls.
166