  We report numerical detection of new type of localized structures in the
frame of Majda-McLaughlin-Tabak (MMT) model adjusted for description of
essentially nonlinear gravity waves on the surface of ideal deep water. These
structures -- quasibreathers, or oscillating quasisolitons -- can be treated as
groups of freak waves closely resembling experimentally observed "Three
Sisters" wave packs on the ocean surface. The MMT model has quasisolitonic
solutions. Unlike NLSE solitons, MMT quasisolitons are permanently backward
radiating energy, but nevertheless do exist during thousands of carrier wave
periods. Quasisolitons of small amplitude are regular and stable, but
large-amplitude ones demonstrate oscillations of amplitude and spectral shape.
This effect can be explained by periodic formation of weak collapses, carrying
out negligibly small amount of energy. We call oscillating quasisolitons
"quasibreathers".
