Strong Low Spins Up Off Southeast Coast

A strong non-tropical low pressure system spun up off the Southeast Coast of the U.S. on Thursday and there is some possibility that it could eventually develop subtropical or tropical characteristics.   At 4:00 p.m. EST on Thursday the low pressure system was centered near latitude 29.0°N and longitude 74.0°W which put it about 425 miles (685 km) west-southwest of Bermuda.  The low was moving toward the east-northeast at 18 m.p.h. (29 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 994 mb.

The low pressure system exhibits the structure of an occluded extratropical cyclone.  An occluded front coils away from the low until it splits into a warm front and a cold front.  Drier air is being pulled around the western and southern sides of the low and a dry slot has formed in the southeastern quadrant of the storm.  However, upper level divergence is pumping mass away from the center of the low and the surface pressure decreased quickly on Thursday afternoon.

The low is in an environment that is not favorable for the classical scenario of formation of a tropical cyclone.  It is moving over water where the Sea Surface Temperature (SST) is near 25°C and strong upper level winds are creating significant vertical wind shear.  However, research has shown that it is possible to get a transition to a subtropical or tropical cyclone over cooler SSTs, when a low pressure system moves into an area where the wind shear is less.

A trough over the southeastern U.S. is steering the low pressure system toward the east-northeast and that general motion is expected to continue during the next day or two.  An upper level ridge is forecast to move north of the low pressure system in a couple of days.  The upper level ridge is expected to steer the low pressure system toward the east-southeast early next week.

If the low pressure system takes the expected track, it could eventually move over slightly warmer SSTs and into an area where there is less vertical wind shear.  The more favorable environment could cause the structure of the low to change into a more subtropical or tropical form.  The National Hurricane Center is giving the low a 10% chance of transitioning into a subtropical cyclone during the next 48 hours and a 30% chance that it makes that transition during the next five days.

Tropical Storm Pali Forms Southwest of Hawaii

A surface circulation organized quickly on Thursday in an area of thunderstorms southwest of Hawaii and the Central Pacific Hurricane Center designated the system as Tropical Storm Pali.  At 4:00 p.m. EDT on Thursday the center of Tropical Storm Pali was located at latitude 4.7°N and longitude 171.2°W which put it about 1450 miles (2335 km) southwest of Honolulu, Hawaii.  Pali was moving toward the north-northwest at 7 m.p.h. (11 km/h).  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 1000 mb.

Several well formed spiral bands developed within a large area of thunderstorms and the system exhibited sufficient organization to be classified as a tropical storm.  Two of the inner spiral bands appear to be wrapping around the center of circulation and the inner core of Tropical Storm Pali is organizing quickly.  A partial eyewall may be forming around the southern and western sides of the center of circulation.  Thunderstorms near the core of Pali are generating upper level divergence, which is pumping out mass.

The environment surrounding Tropical Storm Pali is favorable for further intensification.  It is moving over water where the Sea Surface Temperatures are near 29°C.  An upper level ridge east of Pali is generating southeasterly winds over the top of the tropical storm, but the vertical wind shear is not too strong.  Pali is likely to intensify further during the next 24 hours.  A period of rapid intensification may be possible, if the inner core consolidates around an eye.

A subtropical ridge east of Pali is steering the tropical storm toward the north-northwest and that general motion is expected to continue.  However, the winds steering the storm are not too strong, and it may not move much during the next several days.

Although the historical record of tropical storms over the Central Pacific is relatively short, it appears that Tropical Storm Pali may have reached tropical storm intensity at a lower latitude than any other tropical storm on record did in that region.

Tropical Cyclone Ula Bringing Strong Wind to SE Fiji

Tropical Cyclone Ula is bringing strong winds, heavy rain and high surf to the extreme southeastern islands of Fiji.  At 4:00 p.m. EST on Saturday the center of Tropical Cyclone Ula was located at latitude 19.4°S and longitude 178.0°W which put it about 265 miles ( 430 km) east-southeast of Suva, Fiji.  Ula was moving toward the southwest at 9 m.p.h. (15 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 961 mb.  Tropical Cyclone Ula was the equivalent of a Category 2 hurricane on the Saffir-Simpson Scale.

The inner core structure of Tropical Cyclone Ula changed on Saturday and it may have gone through an eyewall replacement cycle.  Ula started the day with a small pinhole eye, but recent visible satellite imagery indicates that it has a larger, symmetrical eye.  Even though the inner core structure has changed, Tropical Cyclone Ula maintained its intensity.  The structure of Ula is still symmetrical, but most of the stronger thunderstorms are south and west of the center of circulation.

Tropical Cyclone Ula remains in an environment that is favorable for intensification.  It is over water where the Sea Surface Temperature (SST) is near 28°C.  The upper level winds are light and there is not much vertical wind shear.  The favorable environment could allow Ula to maintain its intensity for another 12 to 24 hours.  After that time the tropical cyclone will move into an area where the SSTs are cooler and the upper level winds are stronger.  Cooler water and more vertical wind shear will cause Tropical Cyclone Ula to weaken.

A subtropical ridge is steering Tropical Cyclone Ula toward the southwest.  Ula is nearing the western end of the ridge and it is likely to turn more toward the south in a day or two.  The center of Tropical Cyclone Ula is near Vatoa, Ogea Levu and Ogea Driki.  It is bringing strong winds, heavy rain and large waves to those islands.  It will move near Ono-i-lau, Tuvana-i-colo and Tuvana-i-ro during the next few hours and conditions will get worse on those islands.

Tropical Cyclone Ula Bringing Wind and Rain to Northern Tonga

Tropical Cyclone Ula is bringing wind and rain to islands in northern Tonga.  At 10:00 p.m. EST on Friday the center of Tropical Cyclone Ula was located at latitude 18.3°N and longitude 175.6°W which put it about 100 miles (160 km) north-northwest of Tongatapu, Tonga.  Ula was moving toward the west-southwest at 12 m.p.h. (19 km/h).  The maximum sustained wind speed was 115 m.p.h. (150 km/h) and there were wind gusts to 135 m.p.h. (215 km/h).  The minimum surface pressure was 959 mb.

Lupepau’u airport on Vava’u reported maximum sustained winds of 65 m.p.h. (105 km/h) and wind gusts to 100 m.p.h. (160 km/h) when the center Tropical Cyclone Ula passed north of it.  Ula also brought strong winds and heavy rain to Tafahi, Fonaulei and Toku in northern Tonga.

Tropical Cyclone Ula intensified quickly during the past few hours and a pinhole eye is visible on conventional satellite images.  The eye is surrounded by a tight ring of strong thunderstorms.  Several spiral bands are rotating around the center of Ula.  One of the primary rainbands may be wrapping around the pinhole eye and concentric eyewalls may be developing.  Thunderstorms in the core of Tropical Cyclone Ula are generating upper level divergence that is pumping out mass in all directions.

Tropical Cyclone Ula is in an environment favorable for intensification.  Ula is moving over water where the Sea Surface Temperature (SST) is near 28°C.  The upper level winds are relatively light and there is not much vertical wind shear.  Ula could intensify further during the next few hours, although an eyewall replacement cycle could cause fluctuations in intensity.  Tropical Cyclone Ula could move into an area where the upper level winds are stronger in 24 to 48 hours.  Ula will also move over cooler SSTs in several days.  The combination of more wind shear and cooler SSTs will weaken the tropical cyclone.

A subtropical ridge is steering Tropical Cyclone Ula toward the west-southwest and that general motion is expected to continue for another day or so.  After that time Ula will reach the western end of the ridge and turn more toward the south.  On its expected track Tropical Cyclone Ula could be approaching the southeastern islands of Fiji in about 24 hours.

Tropical Cyclone Ula Becomes Equivalent of Cat. 2 Hurricane South of Samoa

Tropical Cyclone Ula intensified quickly Wednesday into the equivalent of a Category 2 hurricane on the Saffir-Simpson Scale.  At 4:00 p.m. EST on Wednesday the center of Tropical Cyclone Ula was located at latitude 16.3°N and longitude 170.4°W which put it about 135 miles (220 km/h) south-southeast of Pago Pago, Samoa.  Ula was moving toward the southwest at 5 m.p.h. (8 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 961 mb.

Tropical Cyclone Ula has a small, well organized inner core.  An eye has appeared intermittently on satellite imagery.  Thunderstorms near the core are generating upper level divergence which is pumping out mass and allowing the surface pressure to decrease.

Tropical Cyclone Ula is moving through an environment favorable for intensification.  It is over water where the Sea Surface Temperature is near 28.5°C.  The upper level winds are not very strong and there is not much vertical wind shear.  Ula could intensify a little more during the next 24 hours.

A subtropical ridge is steering Tropical Cyclone Ula toward the southwest and a general west-southwesterly motion is expected to continue during the next several days.  Ula is centered between Samoa, Niue and Tonga.  On its anticipated track Tropical Cyclone Ula will approach Tonga in about 24 hours.  It could be approaching Fiji in about three days.  Tropical Cyclone Ula is capable of bringing strong winds, high surf and heavy rain to the islands in its path.

Tropical Depression 09C Forms Near Equator

Sufficient evidence of a surface center of circulation within a broad area of thunderstorms near the Equator prompted the Central Pacific Hurricane Center to classify the system as Tropical Depression 09C.  At 10:00 p.m. EST on Wednesday the center of Tropical Depression 09C (TD09C) was located at latitude 2.8°N and longitude 177.8°W which put it about 1850 miles (2975 km) southwest of Honolulu, Hawaii.  TD09C was moving toward the west-northwest at 8 m.p.h.  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (75 km/h).  The minimum surface pressure was 1001 mb.

The circulation of Tropical Depression 09C is not particularly well organized and there may be multiple small centers inside the larger circulation of the system.  One small center of circulation is near a cluster of thunderstorms in the northern half of the circulation and that center is currently being designated as the center of TD09C.  Another circulation center is near latitude 1.0°N and longitude 174.6°W, but there are no thunderstorms near that center.  The main area of thunderstorms is north of the official center of circulation.  There are a few partial spiral bands northeast of the center of the depression.

The environment around TD09C is only marginal for intensification.  The depression is moving over water where the Sea Surface Temperatures are near 30°C.  So, there is plenty of energy in the upper ocean to support intensification.  However, a strong upper level ridge east of TD09C is generating strong southeasterly winds over the top of the depression.  The strong vertical wind shear is contributing to the poor organization of TD09C.  The wind shear is likely to inhibit intensification during the next several days.

A subtropical ridge east of TD09C is expected to steer the depression slowly toward the west-northwest during the next few days.  The actual track of TD09C could be somewhat erratic, especially if some of the small centers of circulation dissipate and additional centers form in clusters of thunderstorms that develop.  On its anticipated track Tropical Depression 09C could approach Tarawa in about three days and it could be approaching the Marshall Islands this weekend.

The most remarkable thing about Tropical Depression 09C is that is developed so close to the Equator.  Conventional wisdom often says that tropical cyclones cannot form near the Equator because the Coriolis effect is too small.  However, although tropical cyclones are rare near the Equator, Tropical Depression 09C is another example that they can form in that region.

Tropical Cyclone Ula Forms East of Samoa

A well-defined center of circulation consolidated within a very large area of thunderstorms straddling the Equator near the International Date Line and the system was classified as Tropical Cyclone Ula (06P).  At 5:00 a.m. EST on Wednesday the center of Tropical Cyclone Ula was located at latitude 12.5°S and longitude 166.6°W which put it about 325 miles (525 km) east-northeast of Pago Pago, Samoa.  Ula was moving toward the south-southeast at 15 m.p.h. (24 km/h).  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 991 mb.

Thunderstorms in a spiral rainband are wrapping around the center of circulation and microwave satellite imagery has suggested that an eye may be forming in Tropical Cyclone Ula.  Additional spiral bands are developing in the outer portion of the circulation.  The thunderstorms near the center of circulation are generating upper level divergence which is pumping out mass, especially to the east of the center of Ula.

Tropical Cyclone Ula is in an environment that is favorable for intensification.  It is over water where the Sea Surface Temperatures are between 28°C and 29°C.  The upper level winds are light and there is not much vertical wind shear.  Ula is likely to continue to intensify as the core of the circulation consolidates and it could become the equivalent of a hurricane within 24 to 36 hours.

Ula is currently being steered to the south-southeast by a subtropical ridge which is located east of the tropical cyclone.  The ridge is expected to intensify and extend westward.  If it does so, then the building ridge will cause Tropical Cyclone Ula to turn toward the southwest.  On its anticipated track the center of Tropical Cyclone could pass south of Samoa in 24 to 48 hours and it could approach Fiji in four or five days.

Tropical Cyclone Ula could bring strong winds and heavy rain to any island it passes near.

Tropical Low Forms Over Northern Australia

A distinct center of circulation consolidated within a broader area of low pressure near the northern coast of Australia.  The Australian Bureau of Meteorology designated the system as a Tropical Low.  At 10:00 p.m. EST on Saturday the center of the Tropical Low was located at latitude 14.7°N and longitude 132.7°E which put it about 35 miles (55 km) east-southeast of Katherine, Australia and about 135 miles (220 km) west of Ngukurr.  The Tropical Low was moving toward the east at 3 m.p.h. (5 km).  The maximum sustained wind speed was 30 m.p.h. (45 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1005 mb.

The atmospheric environment around the Tropical Low would be favorable for the development of a tropical cyclone.  The upper level winds are light and there is not much vertical wind shear.  An upper level anticyclone over the Tropical Low is providing a source of upper level divergence, which is pumping out mass.  However, the Tropical Low is over land which is preventing the development of a tropical cyclone.  As long as the Tropical Low remains over land, it will not develop into a tropical cyclone.  However, if the Tropical Low emerges over the Gulf of Carpentaria in a day or so, it could develop into a tropical cyclone.

A ridge in the middle levels of the atmosphere is steering the tropical low toward the east and that general motion is expected to continue for another 24 to 48 hours.  On its anticipated track the Tropical Low could emerge over the southwestern Gulf of Carpentaria south of Port Roper in 24 to 36 hours.

Although the Tropical Low is moving over land, it will still draw in enough moisture to be capable of producing locally heavy rain.  Flooding may be possible in some locations.

Typhoon Melor Making Landfall on Mindoro as Equivalent of Cat. 4 Hurricane

Typhoon Melor intensified on Monday and it is making landfall on Mindoro in the Philippines as the equivalent of a Category 4 Hurricane on the Saffir-Simpson Scale.  At 10:00 p.m. EST on Monday the center of Typhoon Melor was located at latitude 13.0°N and longitude 121.5°E which put it about 20 miles (32 km) southeast of Calapan and about 125 miles (205 km) south-southeast of Manila, Philippines.  Melor was moving toward the west at 8 m.p.h. (13 km/h).  The maximum sustained wind speed was 140 m.p.h. (230 km/h) and there were wind gusts to 170 m.p.h. (270 km/h).  The minimum surface pressure was 939 mb.

The core of Typhoon Melor passed just north of Samar and it quickly moved over the southeastern tip of Luzon.  Since the core stayed mainly over water, the circulation was not seriously disrupted by the increased friction that would have occurred if it had moved over land.  As a result, the core Typhoon Melor was intact when it moved over the Sibuyan Sea.  The circulation was able to extract energy from the warm water of Sibuyan Sea.  Melor was in an area where the upper level winds were light and there was little vertical wind shear.  The favorable environment allowed the typhoon to intensify further on Monday and Melor reached the equivalent of a Category 4 hurricane.

The center of Typhoon Melor is making a landfall on the northeast coast of Mindoro.  Since the core of Melor will be moving over the island of Mindoro during the next few hours, the typhoon should start to weaken.  Melor will likely still be a typhoon when the center emerges over the South China Sea.  A strong surge of cold, dry air from the north will increase vertical wind shear around Typhoon Melor in 24 to 36 hours.  The dry air and increased wind shear will weaken Melor more rapidly after that occurs.

A subtropical ridge is steering Typhoon Melor toward the west and that general motion is expected to continue for another 24 to 36 hours.  After that time a weakening Melor will be steered by the flow closer to the surface, which should start to push it toward the southwest.

Typhoon Melor will bring very strong winds and heavy rain to Mindoro and southern Luzon.  The core of Melor should stay south of Manila, but locally heavy rain may be possible.  Heavy rain could also cause flooding and mudslides in areas of steep terrain.

Strong Typhoon Melor Along Coast of Samar Heading for SE Luzon

Typhoon Melor reached the Philippines on Sunday and it was moving along the north coast of Samar toward southeastern Luzon.  At 10:00 p.m. EST on Sunday the center of Typhoon Melor was located at latitude 12.6°N and longitude 125.3°E which put it about 20 miles (32 km) north of Laoang, Philippines and about 100 miles (160 km) east-southeast of Legaspi in southeastern Luzon.  Melor was moving toward the west at 13 m.p.h. (21 km/h).  The maximum sustained wind speed was 130 m.p.h. (210 km/h) and there were wind gusts to 160 m.p.h. (260 km/h).  The minimum surface pressure was 949 mb.

Typhoon Melor has been moving through an environment favorable for intensification.  The Sea Surface Temperatures were near 28°C and there has been little vertical wind shear.  However, the circulation is starting to interact with the Philippines.  The southwestern quarter of the circulation is over Samar.  However, since the core of the circulation is north of the coast of Samar, Melor has remained a strong typhoon.  The circulation of Typhoon Melor is likely to retain much of its integrity until the center makes landfall in southeastern Luzon near Sorsogon.  Melor could remain at typhoon intensity for another 24 hours.  However, eventually the increased friction will slow the portions of the circulation that move over land and Melor will weaken to a tropical storm.

A subtropical ridge is steering Typhoon Melor slightly north of due west and that general motion is expected to continue for several more days.  On its anticipated track the core of Typhoon Melor will pass north of Samar.  It will make landfall on extreme southeastern Luzon near Sorsogon in a few hours.  The center of Melor should pass south of Legaspi before moving over the Sibuyan Sea.  It could move south of Manila in about 36 hours as a tropical storm.

Melor is a strong typhoon and it could bring strong winds and heavy rain to northern Samar, southeastern Luzon, the islands around the Sibuyan Sea and Mindoro.  Heavy rain could cause flooding and trigger mudslides, especially in areas of steep terrain.