Monthly Archives: May 2015

Dolphin Becomes a Typhoon and Heads Toward Guam

Tropical Storm Dolphin moved into a more favorable environment and intensified into a typhoon on Tuesday.  At 11:00 p.m. EDT on Tuesday the center of Typhoon Dolphin was located at latitude 10.2°N and longitude 155.8°W which put it about 350 miles east-northeast of Chuuk and about 810 miles east-southeast of Guam.  Dolphin was moving toward the west at 8 m.p.h.  The maximum sustained wind speed was 75 m.p.h. and there were gusts to 90 m.p.h.  The minimum surface pressure was 974 mb.

Dolphin moved closer to the axis of an upper level ridge and the vertical wind shear which was inhibiting its intensification diminished.  Since Dolphin is over water where the Sea Surface Temperature is near 29°C, the decreased shear allow it to intensify into a typhoon.  Dolphin has a small well organized core circulation with a tiny eye at its center.  Spiral bands of thunderstorms radiate out from the center.  The upper level outflow produced by those thunderstorms has increased and the removal of mass is allowing the surface pressure to decrease.  Dolphin is expected to remain in a region of modest vertical wind shear and further intensification is likely.  A period of rapid intensification is possible.

A subtropical ridge is steering Dolphin toward the west.  The ridge is expected to steer it toward the west-northwest during the next two or three days.  On its anticipated track Dolphin would approach Guam in 48 to 60 hours and it could be a significant typhoon at that time.

 

Tropical Storm Dolphin Moving West and Organizing Slowly

Tropical Storm Dolphin turned toward the west on Monday and showed signs of more organization.  At 11:00 p.m. EDT on Monday the center of Tropical Storm Dolphin was located at latitude 10.3°N and longitude 158.0°E which put it about 490 miles east-northeast of Chuuk and about 950 miles east-southeast of Guam.  Dolphin was moving toward the west at 8 m.p.h.  The maximum sustained wind speed was 50 m.p.h. and there were gusts to 65 m.p.h.  The minimum surface pressure was 989 mb.

Dolphin is moving over water where the Sea Surface Temperature (SST) is near 29°C.  Satellite imagery suggests that the circulation became more symmetrical although many of the stronger thunderstorms are west of the center of circulation.  A strong upper level ridge is located northwest of Dolphin and it is generating easterly winds winds over the top of the circulation.  The vertical wind shear may be the reason why the stronger thunderstorms are west of the center.  The upper level ridge is also contributing to an outflow channel to the southwest of Dolphin which cold pump out more mass.  The vertical wind shear is inhibiting the intensification of Dolphin.  However, as the tropical storm moves farther west, it could move into an area where the upper level winds are lighter.  Given the warm SSTs, a decrease in shear would lead to more intensification.

A subtropical ridge is expected to steer Dolphin toward the west during the next two or three days.  A turn toward the west-northwest will be possible later in the week if a weakness develops in the ridge.  On the anticipated track Dolphin could approach Guam in 48 to 60 hours and it could be a typhoon by that time.

Typhoon Noul Expected to Head Toward Okinawa

Typhoon Noul is expected to pass east of Taiwan and move toward Okinawa on Monday.  At 11:00 p.m. EDT on Sunday the center of Typhoon Noul was located at latitude 21.2°N and longitude 122.4°E which put it about 260 miles south-southeast of Taipei, Taiwan, about 240 miles south-southwest of Ishigaki and about 550 miles southwest of Naha, Okinawa.  Noul was moving toward the north at 11 m.p.h.  The maximum sustained wind speed was 120 m.p.h. and there were gusts to 150 m.p.h.  The minimum surface pressure was 944 mb.

Noul will be moving over increasingly cooler Sea Surface Temperatures (SSTs) as it moves northeastward on Monday.  In addition, it will move into an area where stronger westerly winds are blowing in the upper levels of the atmosphere.  Cooler SSTs and increasing vertical wind shear will cause Noul to weaken steadily.  However, it could still be a typhoon when it passes near Okinawa.

Noul is moving around the western end of the subtropical ridge that has been steering it.  As it moves farther to the north, it will be steered by the mid-latitude westerly winds and Noul will accelerate toward the northeast.  Noul is like to make a transition to an extratropical cyclone when it passes south of Japan.

Tropical Storm Dolphin Expected to Turn West and Head Toward Guam

Tropical Storm Dolphin (07W) has been meandering around within a much larger region of low pressure west of the International Dateline, but it is expected to take a turn toward the west on Monday.  At 10:00 p.m. EDT on Sunday the center of Tropical Storm Dolphin was located at latitude 9.3°N and longitude 159.4°E which put it about 180 miles north-northeast of Pohnpei and about 1040 miles east-southeast of Guam.  Dolphin was moving toward the north-northwest at 10 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.  The minimum surface pressure was 993 mb.

An upper level ridge northeast of Dolphin is producing easterly winds over the top of the circulation and is creating moderate vertical wind shear.  The wind shear is contributing to an asymmetrical circulation where most of the thunderstorms are on the western side.  The shear is inhibiting further organization of the circulation and has kept Dolphin as a minimal tropical storm.  Dolphin is over warm Sea Surface Temperatures and it has the potential to intensify if the wind shear decreases.

A subtropical ridge is expected to build north of Dolphin and to steer it mainly toward the west for much of the coming week.  On its expected track Dolphin could approach Guam in about four days.

Tropical Storm Ana Makes Landfall

The center of Tropical Storm Ana officially made landfall at 6:00 a.m. EDT on Sunday near Myrtle Beach, South Carolina.  Ana was officially a tropical storm at the time of landfall with maximum sustained winds of 45 m.p.h.  This is one of the earliest landfalls of a tropical storm in the U.S. in the historical record.  Ana moved inland slowly and it has weakened to a tropical depression.  At 2:00 p.m. EDT on Sunday the center of Tropical Depression Ana was located at latitude 34.1°N and longitude 78.9°W which put it about 30 miles north of Myrtle Beach, South Carolina.  Ana was moving toward the northeast at 5 m.p.h.  The maximum sustained wind speed was 35 m.p.h. and there were gusts to 45 m.p.h.  The minimum surface pressure was 1006 mb.  The Tropical Storm Warning for the portion of the coast from South Santee River, South Carolina to Cape Lookout, North Carolina has been discontinued.

The slow movement of Ana is creating the potential for locally heavy rain.  There has been some beach erosion as well, but generally the impacts have been minor.  An upper level trough approaching from the west is expected to steer Ana back out into the Atlantic.  However, strong vertical wind shear and cool Sea Surface Temperatures are expected to prevent significant redevelopment when Ana moves back over water.

Typhoon Noul Equivalent of Category 5 Hurricane

Typhoon Noul moved into an area with very little vertical wind shear and intensified into the equivalent of a Category 5 hurricane on the Saffir-Simpson Scale on Saturday.  At 11:00 p.m. EDT on Saturday Typhoon Noul was located at latitude 17.4°N and longitude 123.1°E which put it about 130 miles east of Tuguegarao and about 85 miles southeast of Escarpada Point on the northeastern tip of Luzon.  Noul was moving toward the north-northwest at 12 m.p.h.  The maximum sustained wind speed was 160 m.p.h. and there were gusts to 195 m.p.h.  The minimum surface pressure was 918 mb.

Noul is at the western end of the subtropical ridge that has been steering it toward the northwest.  It should gradually turn more toward the north on Sunday.  The anticipated track will take the center of Noul very close to the northeastern tip of Luzon in a few hours.  As it moves northward, it will start to be affected by westerly winds in a day or so.  Those winds will turn it more toward the northeast and it could affect some of the southern islands of Japan early next week.

As Noul moves toward the north it will move over cooler Sea Surface Temperatures  (SSTs).  In addition the upper level westerly winds will create more vertical wind shear over Noul.  The combination of cooler SSTs and more vertical wind shear will cause Noul to weaken throughout the next few days.  However, if could still be a typhoon when it passes by Okinawa in about 48 hours.

Noul could bring strong winds and heavy rain to the northeastern tip of Luzon on Sunday.  Mudslides could be a possibility in locations that receive heavy rain.

 

Ana Transitions to a Tropical Storm

As Subtropical Storm Ana sat over the relatively warm Sea Surface Temperatures of the Gulf Stream, it drew energy from the upper ocean.  More thunderstorms developed near the center of circulation and condensation released latent energy which warmed the middle and upper levels.  As a result, the circulation became more circularly symmetrical and eventually some upper level outflow developed at the top of the system. As a result of the structural changes, Ana made a transition from a subtropical storm to a tropical storm.

At 11:00 a.m. EDT on Saturday the center of Tropical Storm Ana was located at latitude 32.7°N and longitude 77.9°W which put it about 90 miles southeast of Myrtle Beach, South Carolina and about 105 miles south of Wilmington, North Carolina.  Ana was moving toward the northwest at 3 m.p.h.  The maximum sustained wind speed was 60 m.p.h. and there were gusts to 70 m.p.h.  The minimum surface pressure was 1001 mb.

A Tropical Storm Warning remains in effect from South Santee River, South Carolina to Cape Lookout, North Carolina.  A Tropical Storm Watch is in effect from Edisto Beach to South Santee River, South Carolina.

As the high pressure system that has been blocking the forward progress of Ana moves eastward, the tropical storm will move toward the coast.  It is likely to make landfall near the border of South Carolina and North Carolina on Sunday morning.  An upper level trough approaching from the west will turn Ana toward the northeast and sweep it out to sea after it makes landfall.

Ana is still over the relatively warm water of the Gulf Stream and it is likely to maintain its intensity on Saturday.  When Ana moves north of the Gulf Stream, it will cross over cooler water.  In addition, the approaching upper level trough will begin to generate some vertical wind shear over Ana.  The effects of cooler water and more wind shear mean that Ana will likely be weakening as it approaches the coast.  It will bring some wind, locally heavy rain and beach erosion, but the impacts should be minor in most locations.

Typhoon Noul Approaching the Philippines

Typhoon Noul continued to move steadily toward the west-northwest on Friday and it is approaching the northeastern Philippines.  At 3:00 pm. EDT on Friday the center of Typhoon Noul was located near latitude 13.9°N and longitude 127.0°E which put it about 300 miles east of Labo and about 480 miles east-southeast of Tuguegarao in the Philippines.  Noul was moving toward the west-northwest at 14 m.p.h.  The maximum sustained wind speed was 120 m.p.h. and there were gusts to 150 m.p.h.  The minimum surface pressure was 944 mb.  Noul is the equivalent of a Category 3 hurricane on the Saffir-Simpson Scale.

Noul is being steered to the west-northwest by a subtropical ridge located northeast of it.  As Noul nears the western end of the ridge, it is expected to begin to move more toward the northwest.  As Noul approaches the northeastern coast of Luzon, an upper level trough to the west is expected to turn it more toward the north.  The timing of the turn is still uncertain which makes the track forecast more difficult.  On its projected track Noul would approach northeastern Luzon in about 30 hours.

Noul is over Sea Surface Temperatures near 29°C and there is not much vertical wind shear.  However, there are fewer thunderstorms in the northwestern portion of the circulation and the could be some drier air in that region.  The environment is favorable for intensification but large changes in Noul’s intensity are not expected.  Noul is expected to be a significant typhoon when it approaches Luzon and it could bring strong winds and locally heavy rain to that region.  The heavy rain could lead to mudslides in areas where the slopes are steeper.

Tropical Storm Warning Issued for Ana

The National Hurricane Center has issued a Tropical Storm Warning for the portion of the coast from South Santee River, South Carolina to Surf City, North Carolina.  A Tropical Storm Watch remains in effect from Edisto Beach to South Santee River, South Carolina and from Surf City to Cape Lookout, North Carolina.

At 11:00 a.m. EDT on Friday the center of Subtropical Storm Ana was located at latitude 31.5°N north and longitude 77.3°W which put it about 250 miles east of Savannah, Georgia, about 190 miles east-southeast of Charleston, South Carolina and about 180 miles south-southeast of Wilmington, North Carolina.  Ana was nearly stationary.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.  The minimum surface pressure was 1001 mb.

Thunderstorms are forming on the southern and eastern sides of the circulation and Ana is beginning to look more like a tropical cyclone on satellite images.  It could slowly make a transition to a tropical storm during the next several days.

A high pressure system north of Ana is expected to move slowly eastward and steer Ana toward the coast during the next two or three days.  After that time an upper level trough approaching from the west is expected to steer Ana to the northeast and out to sea.

A combination of marginal Sea Surface Temperatures, drier air and some vertical wind shear is expected to limit the potential for intensification.  However, some modest intensification is possible and the surface pressure has decreased slightly in recent hours.

 

Subtropical Storm Ana Forms Off Southeast U.S. Coast

Thunderstorms developed closer to a broad area of low pressure off the southeast U.S. coast and the National Hurricane Center (NHC) classified it as Subtropical Storm Ana.  At 11:00 p.m. EDT on Thursday the center of Subtropical Storm Ana was located at latitude 31.5°N and longitude 77.6°E which put it about 250 miles east of Savannah, Georgia, about 180 miles southeast of Charleston, South Carolina and about 200 miles south of Wilmington, North Carolina.  Ana was moving toward the north at 2 m.p.h.  The maximum sustained wind speed was 45 m.p.h. and there were gusts to 60 m.p.h.  The minimum surface pressure was 1004 mb.  A Tropical Storm Watch has been issued for the portion of the coast from Edisto Beach, South Carolina to Cape Lookout, North Carolina.

More thunderstorms are being generated near the center of circulation, but the strongest winds are about 90 miles from the center.  So, the structure does not match a classical tropical cyclone where the strongest winds are closer to the center and NHC classified it as a subtropical storm.  The center of circulation is over Sea Surface Temperatures (SSTs) near 26°C which are warm enough to support the development of a tropical cyclone.  So, Ana could make a transition to a tropical storm during the next 24 to 48 hours.  The upper level winds are lighter and vertical wind shear has decreased.  However, because of the proximity to the coast some drier air is being pulled around the western side of the circulation.  Only modest intensification is expected due to marginal SSTs, some vertical wind shear and drier air.

A high pressure system north of Ana is likely to limit the motion of Ana for the next day or two.  Eventually, the high will shift eastward and an upper level trough approaching from the west will accelerate Ana toward the northeast.  Persistent northeasterly winds along the coast could create problems with beach erosion.  The slow movement also means some locations could receive locally heavy rainfall.