Tropical Cyclone Zena formed near Vanuatu on Tuesday.  After several weaker circulations developed within a large trough of low pressure that extended from Tonga west-northwest to near Vanuatu during the past few days, a stronger center of circulation organized near Espiritu Santo on Tuesday.  Thunderstorms consolidated around the center of circulation and the system was designated at Tropical Cyclone Zena (18P).

At 10:00 p.m. EDT on Tuesday the center of Tropical Cyclone Zena was located at latitude 17.6°S and longitude 173.1°E which put it about 300 miles (480 km) west of Nadi, Fiji.  Zena was moving toward the east-southeast at 27 m.p.h. (44 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure was 978 mb.

Tropical Cyclone Zena is a small system.  Tropical storm force winds only extend out about 100 miles (160 km) from the center of circulation.  The Hurricane Size Index (HSI) for Zena is only 6.4  A primary rainband wrapped around the center of circulation and a tiny pinhole eye has appeared intermittently on satellite imagery.  There is a circular ring of thunderstorms at the core of Zena.  The outer portion of the circulation is asymmetrical.  Most of the bands of thunderstorms are east of the center of circulation.

The environment around Tropical Cyclone Zena is somewhat favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 29°C to 30°C.  An upper level ridge is generating moderate west-northwesterly winds around the tropical cyclone.  Much stronger upper level winds are south of Tropical Cyclone Zena.  The upper level winds are inhibiting outflow to the west of the center of the circulation, but they did not inhibit intensification on Tuesday.  Rapid motion of Tropical Cyclone Zena toward the east-southeast appears to have offset some of the effects of the vertical wind shear.  Zena could continue to intensify in the short term, but its small size could make it very vulnerable to the effects of vertical wind shear, if the speed of the upper winds increase.

An upper level ridge located northeast of Zena is steering the tropical cyclone rapidly toward the east-southeast.  That general motion is expected to continue for the next several days.  On its anticipated track Tropical Cyclone Zena will be nearing Fiji in about 12 hours and it could be near Tonga in about 36 hours.  The center of Zena and the strongest winds could pass south of Viti Levu on Wednesday.

Tropical Cyclone Zena could bring strong winds to any of the southern islands of Fiji including southern Viti Levu, Beqa, Kadavu, Lau and the Lomaiviti group.  It could also cause heavy rain and floods.  Tropical Cyclone Zena could bring wind and rain to Tonga on Thursday.