Category Archives: South Pacific

Stronger Tropical Cyclone Donna Moves North of Vanuatu

Tropical Cyclone Donna strengthened on Thursday as it moved north of Vanuatu.  The center of Donna passed near the Banks Islands and the Torres Islands and it is currently located northwest of Espiritu Santo.  At 11:00 p.m. EDT on Thursday the center of Tropical Cyclone Donna was located at latitude 13.2°S and longitude 166.0°E which put it about 350 miles (560 km) north-northwest of Port Vila, Vanuatu.  Donna was moving toward the west-southwest at 7 m.p.h. (11 km/h).  The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h).  The minimum surface pressure was 967 mb.

A partial eyewall continued to wrap around the center of circulation, but a well defined eye did not form.  A band of thunderstorms extended about two thirds of the way around the center.  Other bands of showers and thunderstorms were revolving around the core of the circulation.  Thunderstorms near the core of the circulation generated upper level divergence that pumped out mass to the southeast of Tropical Cyclone Donna.

Winds to hurricane/typhoon force extend out about 40 miles (65 km) from the center of circulation and winds to tropical storm force extend out about 140 miles (225 km) from the center.  The Hurricane Intensity Index (HII) is 16.5.  The Hurricane Size Index (HSI) is 13.4 and the Hurricane Wind Intensity Size Index (HWISI) is 29.9.

Tropical Cyclone Donna will move through an area that will be somewhat favorable for intensification.  Donna will move over water where the Sea Surface Temperature is near 30°C.  An upper level ridge east of Donna is producing northerly winds which are blowing toward the top of the tropical cyclone.  The upper level winds are generating moderate vertical wind shear and the shear seems to have slowed the intensification of Donna.  The strength of the upper level winds could decrease and intensification could resume on Friday.  Tropical Cyclone Donna could intensify into the equivalent of a major hurricane during the next 24 to 48 hours.

A subtropical ridge to the south of Donna is steering the tropical cyclone toward the west-southwest and that general motion is expected to continue for about another 24 hours.  Tropical Cyclone Donna will reach the western end of the ridge in about a day or so and it will turn toward the south.  On its anticipated track the center of Tropical Cyclone Donna will pass west of Espiritu Santo.  Guidance from the numerical models suggests the center of Donna could pass between Vanuatu and New Caledonia, but different models are predicting different tracks and so there is more uncertainty in the track at that time.

Tropical Cyclone Donna Moves Toward Vanuatu and Strengthens

Tropical Cyclone Donna moved toward Vanuatu and strengthened into the equivalent of a hurricane/typhoon on Wednesday.  At 8:00 p.m. EDT on Wednesday the center of Tropical Cyclone Donna was located at latitude 12.4°S and longitude 168.2°E which put it about 270 miles (435 km) north-northeast of Port Vila, Vanuatu.  Donna was moving toward the west at 11 m.p.h. (17 km/h).  The maximum sustained wind speed was 85 m.p.h. (135 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 976 mb.

The circulation of Tropical Cyclone Donna organized further on Wednesday.  An eyelike feature appeared on some microwave satellite images.  An eyewall wrapped about two thirds of the way around the western side of the center of circulation.  A primary rainband curled around the southern and western portions of the core of Tropical Cyclone Donna.  Additional bands of showers and thunderstorms formed and revolved around the core of Donna.  Thunderstorms around the core generated strong upper level divergence which pumped out mass and allowed the pressure to decrease quickly.  A stronger pressure gradient force accelerated the air and resulted in faster wind speeds.

Tropical Cyclone Donna will continue to move through a favorable environment during the next several days.  Donna will move over water where the Sea Surface Temperature is near 30°C.  It is currently in an area where the upper level winds are weak and there is little vertical wind shear.  The combination of warm water and little shear will produce further strengthening and Tropical Cyclone Donna could continue to intensify rapidly.  Donna could intensify into the equivalent of a major hurricane within 24 to 48 hours.

Donna is moving around the northern side of a subtropical ridge which is steering the tropical cyclone toward the west.  A general westerly motion is expected to continue for another 24 hours.  After that time Tropical Cyclone Donna will approach the western end of the ridge and it will turn more toward the south.  Guidance from numerical models differs on the timing and location of the turn toward the south.  On its anticipated track the center of Tropical Cyclone Donna could approach some of the islands of northern Vanuatu in about 24 hours.  It could be a significant tropical cyclone at that time.

Tropical Cyclone 18P Develops Northeast of Vanuatu

Tropical Cyclone 18P developed quickly northeast of Vanuatu on Tuesday.  At 8:00 p.m. EDT on Tuesday the center of Tropical Cyclone 18P was located at latitude 12.7°S and longitude 171.7°E which put it about 695 miles (1120 km) north-northeast of Port Vila, Vanuatu.  The tropical cyclone was moving toward the east at 4 m.p.h. (6 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 992 mb.

The circulation of Tropical Cyclone 18P organized quickly on Tuesday.  More thunderstorms formed near the center of circulation and a  primary rainband wrapped around the eastern side of the center.  Additional bands of showers and thunderstorms developed in the outer regions of the circulation.  Thunderstorms near the core of the circulation generated upper level divergence which pumped out mass and allowed the surface pressure to decrease.

Tropical Cyclone 18P will be moving through an environment that will be very favorable for intensification.  It will move over water where the Sea Surface Temperature is near 30°C.  Tropical Cyclone 18P is centered underneath an upper level ridge and the upper level winds are light.  There is little vertical wind shear.  Tropical Cyclone 18P is likely to intensify rapidly and it could become the equivalent of a hurricane/typhoon within 24 hours.  Once an eye and eyewall form, Tropical Cyclone 18P could intensify very rapidly and it could become the equivalent of a major hurricane within 48 to 72 hours.

Tropical Cyclone 18P is moving through an area where the winds are the steering level are weak.  It has been moving slowly toward the east.  A subtropical ridge to the south of Tropical Cyclone 18P is expected to strengthen and it will turn the tropical cyclone toward the west for about 48 to 72 hours.  When Tropical Cyclone 18P nears the western end of the ridge, it will turn toward the south.  On its anticipated track, Tropical Cyclone 18P could approach Vanuatu in about three days and it could be a significant tropical cyclone at that time.

Stronger Tropical Cyclone Cook Nears New Caledonia

Tropical Cyclone Cook strengthened on Sunday as it neared New Caledonia.  At 8:00 p.m. EDT on Sunday the center of Tropical Cyclone Cook was located at latitude 20.3°S and longitude 165.8°E which put it about 150 miles (240 km) north-northwest of Noumea, New Caledonia.  Cook was moving toward the south-southwest at 11 m.p.h. (18 km/h).  The maximum sustained wind speed was 100 m.p.h. (160 km/h) and there were wind gusts to 120 m.p.h. (195 km/h).  The minimum surface pressure was 969 mb.

Tropical Cyclone Cook intensified on Sunday as the organization of the core improved.  A circular eye developed inside a ring of strong thunderstorms.  The fastest winds were occurring in the ring of storms around the eye.  A number of other bands of showers and thunderstorms were revolving around the core of Tropical Cyclone Cook.  Thunderstorms close to the center of circulation were generating upper level divergence which was pumping out mass to the southeast of the tropical cyclone.  Winds to tropical storm force extended out about 180 miles (290 km) from the center of circulation.

Tropical Cyclone Cook moved through an environment favorable for tropical cyclones on Sunday.  It moved over water where the Sea Surface Temperature was near 29°C.  An upper level ridge east of Cook produced northerly winds which were blowing toward the tropical cyclone, but the wind shear was not great enough to inhibit intensification.  Tropical Cyclone Cook should maintain its intensity until it makes landfall in New Caledonia.  Cook will begin to weaken after the center begins to interact with land.

A subtropical ridge east of Cook is steering the tropical cyclone toward the south-southwest.  A southerly motion is expected to bring the center of Tropical Cyclone Cook to New Caledonia on Monday.  The center of Tropical Cyclone Cook is likely to make landfall between Houailou and Thio on the central coast of New Caledonia.

The Hurricane Intensity Index (HII) for Tropical Cyclone Cook is 16.5.  The Hurricane Size Index (HSI) is 16.8 and the Hurricane Wind Intensity Size Index (HWISI) is 33.3.  The indices indicates that Tropical Cyclone Cook is capable of causing serious regional wind damage.  Tropical Cyclone Cook will also produce heavy rain and a chance for flash floods.

Strengthening Tropical Cyclone Cook Brings Wind and Rain to Vanuatu

Strengthening Tropical Cyclone Cook brought wind and rain to Vanuatu on Saturday.  At 11:00 p.m. EDT on Saturday the center of Tropical Cyclone Cook was located at latitude 17.8°S and longitude 167.4°E which put it about 65 miles (105 km) west of Port Vila, Vanuatu.  Cook was moving toward the south at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 70 m.p.h. (110 km/h) and there were wind gusts to 85 m.p.h. (135 km/h).  The minimum surface pressure was 985 mb.

Tropical Cyclone Cook strengthened quickly on Saturday as it moved through central portions of Vanuatu.  A primary rainband wrapped around the center of circulation and a clear area appeared intermittently on satellite imagery.  The strongest winds were occurring in a ring of thunderstorms around the forming eye.  The thunderstorms near the center were generating upper level divergence which was pumping out mass toward the southeast of Tropical Cyclone Cook.  Additional bands of showers and thunderstorms were forming in the eastern half of the circulation.  Winds to tropical storm force extend out about 150 miles (240 km) from the center of circulation.

Tropical Cyclone Cook will move through an environment that will be favorable for intensification during the next 24 to 36 hours.  Cook will move over water where the Sea Surface Temperature (SST) is near 30°C.  An upper level ridge to the east of Cook is generating northerly winds which are blowing toward the tropical cyclone, but the vertical wind shear is minimal.  Warm SSTs and little vertical wind shear will allow Tropical Cyclone Cook to intensify.  A period of rapid intensification could occur after the eye and eyewall are completely formed.  Tropical Cyclone Cook should become the equivalent of a hurricane/typhoon on Sunday.

Tropical Cyclone Cook is moving around the western end of a subtropical ridge.  The ridge is steering Cook a little to the west of due south.  A general south-southwesterly motion is expected to continue for another 24 to 36 hours.  On its anticipated track Tropical Cyclone Cook will move away from Vanuatu and toward New Caledonia.  Tropical Cyclone Cook could approach New Caledonia in about 36 hours.

The core of Tropical Cyclone Cook will continue to bring wind and rain to the area around Port Vila, Vanuatu on Sunday.  Storms in the outer rainbands will bring wind and rain to the southern parts of Vanuatu.  Tropical Cyclone Cook will be the equivalent of a hurricane/typhoon when it nears New Caledonia.  Cook will be capable of causing wind damage and heavy rain could cause flash flooding.

Tropical Cyclone Amos Speeds Past Samoa and Weakens

Tropical Cyclone Amos weakened as it sped past Samoa on Saturday.  At 11:00 p.m. EDT on Saturday the center of Tropical Cyclone Amos was located at latitude 14.0°S and longitude 169.1°W which put it about 15 miles (25 km) north of Luma, Samoa.  Amos was moving toward the southeast at 19 m.p.h. (31 km/h).  The maximum sustained wind speed was 80 m.p.h. (130 km/h) and there were wind gusts to 100 m.p.h. (160 km/h).  The minimum surface pressure was 970 mb.

A ridge of high pressure east of Amos produced strong northwesterly winds which steered the tropical cyclone rapidly to the east-southeast on Saturday.  Those steering winds carried the core of Amos just north of the larger islands of Samoa.  Since hurricane force winds only extended out about 20 miles (30 km) from the center of circulation, the stronger winds stayed mostly over the open water.  A weather station in Pago Pago, Samoa reported a wind gust of 54 m.p.h. (87 km/h).

Tropical Cyclone Amos is currently bringing wind and rain to the Manua Islands of eastern Samoa which include Olosega, Ofu and Ta’u.  The rapid forward motion of Amos means that conditions should improve within a few hours.

The strong northwesterly winds are causing significant vertical wind shear that is rapidly weakening Tropical Cyclone Amos.  Amos is still moving over water where the Sea Surface Temperature is near 30°C, but the vertical wind shear should continue to weaken the tropical cyclone as it moves farther east of Samoa.

Strong Tropical Cyclone Amos Heading Toward Samoa

Tropical Cyclone Amos strengthened as it passed over Iles Wallis and headed toward Samoa on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Cyclone Amos was located at latitude 12.5°S and longitude 175.4°E which put it about 70 miles (115 km) north-northeast of Iles Wallis and about 360 miles (580 km) west-northwest of Pago Pago, Samoa.  Amos was moving toward the east at 11 m.p.h. (18 km/h).  The maximum sustained wind speed was 105 m.p.h. (170 km/h) and there were wind gusts to 125 m.p.h. (205 km/h).  The minimum surface pressure was 956 mb.

The core of the circulation of Tropical Cyclone Amos is small but it is well organized.  There is a ring of the thunderstorms around an eye, but clouds from the taller thunderstorms are obscuring the eye on conventional satellite imagery.  Multiple bands of thunderstorms are rotating around the core of the circulation.  The thunderstorms are generating well developed upper level divergence which is pumping out mass in all directions.

Tropical Cyclone Amos is an environment favorable for further intensification.  It is moving over water where the Sea Surface Temperature is near 30°C.  The winds in the upper levels are weak and there is not much vertical wind shear.  Amos is likely to intensify during the next 24 hours and it could be the equivalent of a major hurricane when it reaches the western part of Samoa.

A ridge of high pressure is expected to steer Tropical Cyclone Amos toward the east-southeast during the nest several days.  On its anticipated track Amos could be approaching the western islands of Samoa in a little over 24 hours.  It could be the equivalent of a major hurricane at that time.

The Hurricane Intensity Index (HII) for Amos is currently 17.8.  The Hurricane Size Index (HSI) is 9.0 and the Hurricane Wind Intensity Size Index (HWISI) is 26.8.  Those indices suggest that the core of Tropical Cyclone Amos will be capable of causing major damage if it moves directly over any of the islands of Samoa.  In addition, Amos will produce locally heavy rain capable of causing flash floods.  It could also generate high waves and surges along the coasts of some of the islands.

Tropical Cyclone Amos to Bring Wind and Rain to Wallis and Samoa

Tropical Cyclone Amos intensified to the equivalent of a hurricane/typhoon on Thursday as it moved eastward across the South Pacific.  At 11:00 p.m. EDT on Thursday the center of Tropical Cyclone Amos was located at latitude 12.4°S and longitude 177.1°W which put it about 80 miles (130 km) northwest of Iles Wallis.  Amos was moving toward the east-northeast at 11 m.p.h. (18 km/h).  The maximum sustained wind speed was 75 m.p.h. (120 km/h) and there were wind gusts to 90 m.p.h. (145 km/h).  The minimum surface pressure 974 mb.

Tropical Cyclone Amos is a small, tightly organized storm.  A primary band of thunderstorms wraps almost entirely around the center of circulation and an eyelike feature is visible intermittently on satellite imagery.  Additional bands of showers and thunderstorms are spiraling around the core of the circulation.  The thunderstorms are generating upper level divergence which is pumping out mass in all directions and causing the surface pressure to decrease.

The environment around Tropical Cyclone Amos is very favorable for further intensification.  It is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are very weak and there is little vertical wind shear.  Amos will continue to intensify on Friday and it could intensify rapidly.

A subtropical ridge north of Amos is steering the tropical cyclone toward the east and that general motion is expected to continue for several more days.  On its anticipated track Amos will pass near Iles Wallis on Friday.  Although the core of strongest winds will pass north of Iles Wallis, It could still bring strong winds, heavy rain and large waves to those islands.  On its anticipated track Amos could be approaching western Samoa within 36 hours.  It could be a very strong tropical cyclone at that time.

Tropical Cyclone Amos Forms North of Fiji

A center of circulation developed within a large area of thunderstorms north of Fiji on Wednesday and the system was designated as Tropical Cyclone Amos.  At 5:00 p.m. EDT on Wednesday the center of Tropical Cyclone Amos was located at latitude 12.5°S and longitude 179.4°W which put it about 145 miles (235 km) northwest of Ile Futuna.  Amos was stationary.  The maximum sustained wind speed was 50 m.p.h. (80 km/h) and there were wind gusts to 65 m.p.h. (105 km/h).  The minimum surface pressure was 989 mb.

The circulation near the core of Tropical Cyclone Amos is still organizing.  A narrow primary band of thunderstorms is wrapping tightly around the core and an eye may be forming at the center of circulation.  Several other thin bands of showers and thunderstorms are rotating around the outer portions of the circulation.  The thunderstorms are generating some upper level divergence, but it is not well developed yet.

The environment is favorable for continued intensification.  Amos is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are not very strong and there is little vertical wind shear.  As the core of the circulation becomes more well organized, it will convert energy from the ocean more efficiently and the wind speeds will increase.  Tropical Cyclone Amos could intensify into the equivalent of a hurricane/typhoon within 24 to 36 hours.

Tropical Cyclone Amos is currently in an area where the steering currents are weak.  An upper level ridge is forecast to develop north of Amos and begin to steer the tropical cyclone toward the east.  On its anticipated track Amos could pass near Iles Wallis in 24 to 36 hours.  It could be approaching Samoa in two or three days.

Tropical Cyclone Zena Shears Apart South of Fiji

Strong upper level winds blew the upper portion of the circulation east of the surface circulation of Tropical Cyclone Zena as it passed south of Fiji.  At 8:00 p.m. EDT on Wednesday the center of Tropical Cyclone Zena was located at latitude 21.5°S and longitude 176.0°W which put it about 60 miles (95 km) west of Nuku’ Alofa, Tonga.  Zena was moving toward the east-southeast at 36 m.p.h. (58 km/h).  The maximum sustained wind speed was 60 m.p.h. (95 km/h) and there were wind gusts to 75 m.p.h. (120 km/h).  The minimum surface pressure was 988 mb.

Although Tropical Cyclone Zena briefly reached hurricane/typhoon intensity on Tuesday, it always consisted of a very small circulation which was very susceptible to vertical wind shear.  When an upper level ridge northeast of Zena increased west-northwesterly winds over the top of the tropical cyclone, those winds blew the upper portion of the circulation east of the center. The circulation of Zena lost its vertical integrity and it was difficult to find a well defined center of circulation at the surface by late Wednesday.  The remnants of Tropical Cyclone Zena are on a trend of rapid weakening.  The vertical wind shear is expected to continue and Zena could dissipate within 24 to 36 hours while it passes south of Niue.