Fiji's metservice says the tropical depression over Fiji is expected to develop into a tropical cyclone near Tonga by today.
The depression, currently over the northern Lau group, is strengthening and moving south east.
A tropical cyclone alert is in place for Ha'apai and Vava'u groups, Niuafo'ou and Niuatoputapu Group.
The duty forecaster, Amit Singh, says it's likely to be named within the next 36 to 48 hours, but there are indications that it won't be a full-strength cyclone.
"We don't expect this system to be a very serious system, if it forms. It may remain a category one."
Amit Singh says people are being advised to expect gale force winds and heavy rain and flooding, and take all necessary precautions.