Cyclone Nancy originated out of a broad area of low pressure within a monsoonal trough northeast of Samoa on February 10.
Initially, the system was nearly stationary within an area of weak steering currents, low wind shear and high sea surface temperatures, exceeding 30 °C (86 °F).
On February 11, a trough briefly increased shear over the system and its nearby twin, the precursor to Cyclone Olaf.
By 0600 UTC on February 12, the system's outflow improved and a small area of deep convection, known as the central dense overcast, developed over the center of circulation.
Later that day, the Regional Specialized Meteorological Centre (RSMC) in Nadi, Fiji upgraded the system to a Category 1 cyclone and gave it the name Nancy while it was located about 485 km (300 mi) east-northeast of Pago Pago, American Samoa.
By this time, the Joint Typhoon Warning Center (JTWC) had also begun issuing advisories on the storm, designating it as Tropical Cyclone 18P.
The storm had undertaken a slow northeast motion early on February 13 before turning southeast in response to a mid-level ridge located northeast of the cyclone.
Convective banding features developed close to the center of circulation as the storm began to undergo explosive intensification.
Around 1200 UTC, the storm attained Severe Tropical Cyclone status as winds reached 120 km/h (75 mph 10-minute winds) and a small, irregularly shaped, eye began to develop.
The JTWC, however, assessed Nancy to have been substantially weaker until 0000 UTC on February 14, at which time they reported a 95 km/h (60 mph) increase in winds, attaining minimal Category 3 status on the Saffir–Simpson Hurricane Scale.

By 1200 UTC on February 14, Nancy attained its peak intensity with winds of 175 km/h (110 mph 10-minute winds) and a barometric pressure of 935 hPa (mbar).
Shortly after, the JTWC assessed Nancy to have peaked with winds of 230 km/h (145 mph 1-minute winds).
Increasing forward motion to the southeast and increasing wind shear caused Nancy to weaken.
Early on February 15, the storm passed directly over Manuae.
Continued weakening took place as a trough approached from the southwest.
By February 16, Nancy weakened below hurricane intensity and turned to the southwest as it began to undergo a Fujiwhara interaction with Cyclone Olaf to the north.

Strong shear associated with the outflow of Cyclone Olaf caused all convection associated with Nancy to be displaced to the southwest on February 16.
Early on February 17, Nancy transitioned into an extratropical cyclone as it entered the area of responsibility of the Tropical cyclone warning centre (TCWC) in Wellington, New Zealand.
Shortly after, the low was absorbed into the larger circulation of Olaf.
However, TCWC Wellington continued to monitor Nancy as a separate system until 1200 UTC on February 18.
Cyclone Nancy originated out of a broad area of low pressure within a monsoonal trough northeast of Samoa on February 10. Initially, the system was nearly stationary within an area of weak steering currents, low wind shear and high sea surface temperatures, exceeding 30 °C (86 °F). On February 11, a trough briefly increased shear over the system and its nearby twin, the precursor to Cyclone Olaf. By 0600 UTC on February 12, the system's outflow improved and a small area of deep convection, known as the central dense overcast, developed over the center of circulation. Later that day, the Regional Specialized Meteorological Centre (RSMC) in Nadi, Fiji upgraded the system to a Category 1 cyclone and gave it the name Nancy while it was located about 485 km (300 mi) east-northeast of Pago Pago, American Samoa. By this time, the Joint Typhoon Warning Center (JTWC) had also begun issuing advisories on the storm, designating it as Tropical Cyclone 18P.
The storm had undertaken a slow northeast motion early on February 13 before turning southeast in response to a mid-level ridge located northeast of the cyclone. Convective banding features developed close to the center of circulation as the storm began to undergo explosive intensification. Around 1200 UTC, the storm attained Severe Tropical Cyclone status as winds reached 120 km/h (75 mph 10-minute winds) and a small, irregularly shaped, eye began to develop. The JTWC, however, assessed Nancy to have been substantially weaker until 0000 UTC on February 14, at which time they reported a 95 km/h (60 mph) increase in winds, attaining minimal Category 3 status on the Saffir–Simpson Hurricane Scale.
By 1200 UTC on February 14, Nancy attained its peak intensity with winds of 175 km/h (110 mph 10-minute winds) and a barometric pressure of 935 hPa (mbar). Shortly after, the JTWC assessed Nancy to have peaked with winds of 230 km/h (145 mph 1-minute winds). Increasing forward motion to the southeast and increasing wind shear caused Nancy to weaken. Early on February 15, the storm passed directly over Manuae. Continued weakening took place as a trough approached from the southwest. By February 16, Nancy weakened below hurricane intensity and turned to the southwest as it began to undergo a Fujiwhara interaction with Cyclone Olaf to the north.
Strong shear associated with the outflow of Cyclone Olaf caused all convection associated with Nancy to be displaced to the southwest on February 16. Early on February 17, Nancy transitioned into an extratropical cyclone as it entered the area of responsibility of the Tropical cyclone warning centre (TCWC) in Wellington, New Zealand. Shortly after, the low was absorbed into the larger circulation of Olaf. However, TCWC Wellington continued to monitor Nancy as a separate system until 1200 UTC on February 18.
Cyclone Nancy