{There ariseth a great storm of wind} (ginetai lailaps
megal(8820)anemou). Mark's vivid historical present again.  Mt 8:24 
has egeneto (arose) and  Lu 8:23  kateb(885c) (came down). Luke
has also lailaps, but Matthew seismos (tempest), a violent
upheaval like an earthquake. Lailaps is an old word for these
cyclonic gusts or storms. Luke's "came down" shows that the storm
fell suddenly from Mount Hermon down into the Jordan Valley and
smote the Sea of Galilee violently at its depth of 682 feet below
the Mediterranean Sea. The hot air at this depth draws the storm
down with sudden power. These sudden storms continue to this day
on the Sea of Galilee. The word occurs in the LXX of the
whirlwind out of which God answered Job ( Job 38:1 ) and in  Jon
1:4 . {The waves beat into the boat} (	a kumata epeballen eis to
ploion). Imperfect tense (were beating) vividly picturing the
rolling over the sides of the boat "so that the boat was covered
with the waves" ( Mt 8:24 ). Mark has it: "insomuch that the boat
was now filling" (h(9373)te (8864)(8820)gemizesthai to ploion). Graphic
description of the plight of the disciples.