Monthly Archives: September 2016

Matthew Rapidly Intensifies Into Category 4 Hurricane

Hurricane Matthew intensified very rapidly into a Category 4 hurricane on the Saffir-Simpson Scale as it moved across the southern Caribbean Sea on Friday.  At 5:00 p.m. EDT on Friday the center of Hurricane Matthew was located at latitude 13.5°N and longitude 71.6°W which put it about 75 miles (120 km) north of Punta Gallinas, Colombia.  Matthew was moving toward the west-southwest at 9 m.p.h. (15 km/h).  The maximum sustained wind speed was 140 m.p.h. (220 km/h). and there were wind gusts t0 165 m.p.h. (265 km/h).  The minimum surface pressure was 949 mb.

The Hurricane Size Index (HII) was 28.3.  The Hurricane Intensity Index (HII) was 13.2 and the Hurricane Wind Intensity Size Index (HWISI) was 41.5.  The indices mean that Hurricane Matthew is very similar in size and intensity to what Hurricane Ike was when Ike was northeast of the Leeward Islands in 2008.  The indices also mean that Hurricane Matthew is capable of producing regional significant wind damage.

Hurricane Matthew is very well organized and it efficiently extracted energy from the warm water of the Caribbean Sea to intensify rapidly on Friday.  It has a circular eye with a diameter of about 15 miles (24 km).  The eye is surrounded by a ring of very tall thunderstorms.  The thunderstorms are pumping out large quantities of mass which allowed the surface pressure to decrease by 44 mb during the past 24 hours.  There additional bands of thunderstorms, mainly in the eastern half of the circulation.

Hurricane Matthew will remain in a very favorable environment while it is over the Caribbean Sea.  It could intensify further.  When hurricanes become as strong as Matthew strong, they sometimes undergo eyewall replacement cycles.  During an eyewall replacement cycle, a hurricane first weakens and then strengthens again when the innermost eyewall dissipates.  If eyewall replacement cycles occur in Hurricane Matthew, then the intensity will fluctuate.

A strong subtropical high pressure system north of Matthew is steering the hurricane toward the west-southwest.  That general motion is expected to continue for another 24 hours.  When Matthew reaches the western end of the subtropical high, it will start to move toward the north.  Guidance from numerical models is still divergent about the details of the turn toward the north.  If the turn is sharper, it could mean that Hurricane Matthew moves toward Haiti.  If the turn is more gradual, it could mean that Matthew heads for Jamaica and eastern Cuba.  The uncertainty is the reason why watches have been posted for both Jamaica and Haiti.

Matthew is a very powerful hurricane.  It is capable of causing regional significant wind damage.  In addition Matthew will produce very heavy rain and the potential for dangerous flash flooding.  There is also the possibility of a significant storm surge along the coast.

Matthew Becomes a Hurricane Over the Eastern Caribbean Sea

Tropical Storm Matthew strengthened into a hurricane on Thursday as it moved over the eastern Caribbean Sea.  At 8:00 p.m. EDT on Thursday the center of Hurricane Matthew was located at latitude 14.2°N and longitude 68.1°W which put it about 150 miles (240 km) north-northeast of Curacao.  Matthew was moving toward the west at 15 m.p.h. (24 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 was 987 mb.

Tropical Storm Watches are in effect for Curacao, Bonaire and Aruba.  The government of Columbia has also issued a Tropical Storm Watch for the portion of the coast from the Columbia/Venezuela border to Riohacha.

The structure of Hurricane Matthew became much better organized on Thursday.  A primary rainband wrapped around the center of circulation.  An eye appears to be forming.  A ring of strong thunderstorms surrounds the eye on all sides except to the south.  Additional bands of thunderstorms developed in the northern and eastern parts of the circulation.  The storms near the eye generated upper level divergence which pumped out mass to the north and east of Hurricane Matthew.  The upper level divergence pumped out enough mass to allow the minimum pressure to decrease by 17 mb during the past 24 hours.

Hurricane Matthew will be moving into an environment that will be favorable for intensification.  It will move over water where the Sea Surface Temperature is near 30°C.  An upper level trough over the western Caribbean Sea and an upper level ridge just east of Matthew are producing southwesterly winds which are blowing across the top of the hurricane.  The vertical wind shear made Hurricane Matthew’s structure asymmetrical earlier today, but the shear has been less in recent hours.  The effect of the wind shear will be to slow the rate of intensification, but it will not prevent intensification.  Hurricane Matthew will pass just north of the cost of South America and drier air could also slow the rate of intensification.

A strong subtropical high pressure system to the north of Matthew is steering the hurricane toward the west and that general motion is expected to continue for about another 48 hours.  When Hurricane Matthew reaches the western end of the ridge, it will turn toward the north.  Guidance from the numerical models continues to be quite divergent about when, where and how sharp the turn will be.  If Hurricane Matthew turns sooner and sharper, it could move over Haiti early next week.  On the other hand, if Matthew turns later and more gradually, it could affect Jamaica and eastern Cuba.  It is too early to know which scenario will eventually occur.

Hurricane Matthew could become a major hurricane over the Caribbean Sea and interests in the Greater Antilles should monitor its progress.

Tropical Storm Chaba Organizes and Moves Toward Okinawa

Tropical Storm Chaba strengthened on Thursday as it started to move toward Okinawa.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Chaba was located at latitude 13.8°N and longitude 138.6°E which put it about 1145 miles (1850 km) southeast of Okinawa.  Chaba was moving toward the west at 14 m.p.h. (22 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 996 mb.

The circulation of Tropical Storm Chaba showed signs of better organization on Thursday.  A primary rainband wrapped around the western and south sides of the circulation.  Additional bands of thunderstorms were forming on the southern and eastern side of Tropical Storm Chaba.  Thunderstorms near the core of Chaba were generating upper level divergence which was pumping mass out to the west, south and east of the tropical storm.

Tropical Storm Chaba is moving into an environment that is favorable for intensification.  It is moving over water where the Sea Surface Temperature (SST) is near 30°C.  An upper level ridge to the north of Chaba is generating easterly winds which are blowing across the northern portion of the tropical storm.  However, those winds are not causing significant vertical wind shear.  The combination of warm SSTs and little vertical wind shear should allow Tropical Storm Chaba to intensify steadily during the next several days.  It could become a typhoon within 24 to 48 hours.  There is a chance that Chaba could become the equivalent of a major hurricane in three or four days.

A subtropical ridge to the north of Chaba is steering the tropical storm toward the west and that general motion is expected to continue in the short term.  When Chaba gets a little closer to the western end of the ridge, it will start to move toward the northwest and when Chaba reaches the western end of the ridge it will turn toward the north.  On it anticipated track Tropical Storm Chaba could be approaching Okinawa and the Ryukyu islands in about three days.  It could be a powerful typhoon at that time.

Tropical Storm Matthew Develops Near the Windward Islands

The National Hurricane Center determined that a surface circulation center formed within Invest 97L on Wednesday morning and it designated the system as Tropical Storm Matthew.  At 11:00 a.m. EDT on Wednesday the center of Tropical Storm Matthew as located at latitude 13.4°N and longitude 60.7°W which put it about 35 miles (55 km) southeast of St. Lucia.  Matthew was moving toward the west at 21 m.p.h. (33 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 1008 mb.

Tropical Storm Warnings have been issued for Guadeloupe, Martinique, Barbados, Dominica, St. Lucia, and St. Vincent and the Grenadines.

The circulation of Tropical Storm Matthew is still organizing and it appears as if the surface center is located southwest of the mid-level center.  There are many more thunderstorms north and east of the center and there are fewer thunderstorms south and west of the center.  The strongest winds are occurring in the bands of thunderstorms northeast of the center of circulation.  The winds are much weaker in the western half of Tropical Storm Matthew.  The stronger thunderstorms northeast of the center of circulation are generating upper level divergence which is pumping mass out to the north and east of Matthew.

Tropical Storm Matthew will be moving into an environment that is favorable for intensification The Sea Surface Temperatures in the eastern and central Caribbean Sea are near 30°C.  The upper level winds are weak and there is not much vertical wind shear.  Even with those favorable conditions, several factors could slow the rate at which Tropical Storm Matthew intensifies.  First, it is moving west at 21 m.p.h. (33 km/h).  Sometimes tropical cyclones generate low level vertical wind shear when they move that quickly.  Second, the asymmetrical distribution of thunderstorms around the circulation of Matthew could prevent the tropical storm form efficiently using the energy it extracts from the ocean.  In addition, if Tropical Storm Matthew moves too close to the northern coast of South America, it could pull in some drier air, which would also slow the rate of intensification.  Even with those potential inhibiting factors, Tropical Storm Matthew is likely to become a hurricane by the end of the week and it could become a major hurricane while it is over the Caribbean Sea.

A subtropical high pressure system to the north of Matthew is steering the tropical storm toward the west and that general motion is expected to continue for several more days.  Tropical Storm Matthew is likely to slow down over the weekend as it gets closer to the western end of the subtropical high.  Matthew will likely turn toward the north during the weekend.  There is a great deal of variability in how quickly and sharply the models predict the turn will be.  Some models forecast a quick sharp turn toward the north that could eventually carry Matthew near Bermuda.  Other models forecast a later slower turn that occurs over the western Caribbean Sea and could take take Matthew closer to the U.S.  It is too early to know which scenario will be the right one.

Tropical Storm Matthew will bring gusty winds and locally heavy rain to the Windward Islands and southern Leeward Islands.  Interests in other parts of the Caribbean Sea, the Bahamas, U.S. and Bermuda should monitor the progress of Tropical Storm Matthew.

Invest 97L Poses Risk for Caribbean Sea

A tropical disturbance designated as Invest 97L poses a potential risk for locations around the Caribbean Sea.  At 8:00 p.m. EDT on Tuesday the center of Invest 97L was located at latitude 13.1°N and longitude 55.3°W which put it about 285 miles (460 km) east of Barbados.  Invest 97L was moving toward the west at 19 m.p.h. (31 km/h).  The maximum sustained wind speed was 35 m.p.h. (55 km/h) and there were wind gusts to 45 m.p.h. (70 km/h).  The minimum surface pressure was 1008 mb.

A U.S. Air Force Reserve Hurricane Hunter aircraft flew a reconnaissance mission into Invest 97L on Tuesday afternoon.  The plane found the there were winds to near tropical storm force, but it could not identify a closed circulation.  The winds on the western side were weaker and the plane was unable to find a surface center.  There does seem to be cyclonic rotation above the surface at least on infrared satellite imagery.

The circulation in Invest 97L is still organizing.  Many of the stronger thunderstorms are forming north and east of the apparent center on satellite imagery.  Rainbands are also forming north and east of the center.  Recent satellite images suggest that some thunderstorms could be developing closer to the center of cyclonic rotation.  The current thunderstorms are generating upper level divergence which is pumping out mass to the north and east of the system.

Invest 97L is moving through an environment that is favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 29°C.  The upper level winds over the majority of the circulation are relatively weak.  An upper level trough over the Caribbean Sea is generating vertical wind shear over the northern fringe of the circulation.  Invest 97L could become a tropical storm at any time.

A subtropical high pressure system to the north of Invest 97L is steering it toward the west and that general motion is expected to continue for another day or two.  On its anticipated track Invest 97L will move through the Windward Islands near Barbados, St. Lucia, Martinique, and Dominica on Wednesday.  It could bring gusty winds and locally heavy rain to those locations.

Tropical Storm Chaba Forms East of Guam

A center of circulation developed within an area of thunderstorms east of Guam on Tuesday and the Japan Meteorological Agency designated the system as Tropical Storm Chaba.  At 11:00 p.m. EDT on Tuesday the center of Tropical Storm Chaba was located at latitude 14.2°N and longitude 147.7°E which put it about 225 miles (360 km) east of Guam.  Chaba was moving toward the west at 17 m.p.h. (27 km/h).  The maximum sustained wind speed was 40 m.p.h. (65 km/h) and there were wind gusts to 50 m.p.h. (80 km/h).  The minimum surface pressure was 1000 mb.

The circulation of Tropical Storm Chaba is still organizing.  The distribution of thunderstorms is asymmetrical.  There are more thunderstorms east of the center of circulation.  Additional thunderstorms are forming west of the center of circulation and some rainbands are developing.  The thunderstorms near the center of Tropical Storm Chaba are generating upper level divergence which is pumping mass out in all directions.

Tropical Storm Chaba is moving through an environment that is favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are light and there is not significant vertical wind shear.  Tropical Storm Chaba is likely to continue to intensify as the circulation gets better organized.  Chaba could become a typhoon later this week.

A subtropical ridge to the north of Chaba is steering the tropical storm toward the west and that general motion is expected to continue for another 24 to 36 hours.  When Tropical Storm Chaba moves farther west, it will get closer to the western end of the subtropical ridge and Chaba is likely to turn more toward the west-northwest.  On its anticipated track Tropical Storm Chaba will move through the Marianas between Guam and Saipan and Tinian on Wednesday.  Chaba could be approaching Okinawa in about five days.

Powerful Typhoon Megi Nearing Landfall on Taiwan

Powerful Typhoon Megi is within a few hours of making landfall on the east coast of Taiwan.  At 11:00 p.m. EDT on Monday the center of Typhoon Megi was located at latitude 23.3°N and longitude 122.6°E which put it about 175 miles (280 km) southeast of Taipei, Taiwan.  Megi was moving toward the northwest at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 115 m.p.h. (185 km/h) and there were wind gusts to 145 m.p.h. (230 km/h).  The minimum surface pressure was 947 mb.

Megi is a large powerful typhoon and it is the equivalent of a major hurricane.  It has a big circular eye with a diameter of about 60 miles (95 km).  Winds to typhoon force extend out about 50 miles (80 km) from the center and winds to tropical storm force extend out over 200 miles (320 km) from the center.

The Hurricane Intensity Index (HII) for Typhoon Megi is 20.6.  The Hurricane Size Index (HSI) is 21.1 and the Hurricane Wind Intensity Size Index (HWISI) is 41.7.  Those indices suggest that Typhoon Megi is capable of causing widespread major wind damage.  The HII for Typhoon Megi is the same as the HII for Hurricane Rita when it made landfall in Louisiana in 2005.  The HSI for Megi is slightly smaller than the HSI for Rita.  Thus, Typhoon Megi is as intense as Hurricane Rita was when it made landfall, but Megi is slightly smaller than Rita was in 2005.

A subtropical ridge is steering Typhoon Megi toward the northwest.  Typhoon Megi will make landfall on the east coast of Taiwan near Hualien in a few hours.  Megi will cross Taiwan and it will make a second landfall on the east coast of China near Quanzhou and Xiamen in about 24 hours.  Typhoon Megi will bring strong winds and very heavy rain to the northern two thirds of Taiwan.  The heavy rain will create a serious risk for flash flooding.  Megi will weaken as it crosses Taiwan,   Typhoon Megi will also bring gusty winds and heavy rain when it reaches the east coast of China.  Typhoon Meranti caused serious damage in parts of Fujian province and Typhoon Megi will bring heavy rain to some of those same areas.  The northern side of Typhoon Megi may also bring gusty winds to the southernmost Ryukyu Islands.

Typhoon Megi Strengthens As It Moves Closer to Taiwan

Typhoon Megi strengthened quickly on Saturday as it moved steadily closer to Taiwan.  At 11:00 p.m. EDT on Saturday the center of Typhoon Megi was located at latitude 19.4°N and longitude 131.0°E which put it about 685 miles (1105 km) east-southeast of Taipei, Taiwan.  Megi was moving toward the west northwest at 14 m.p.h. (22 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 963 mb.

Megi is a large well organized typhoon.  Winds to typhoon force extend out about 50 miles (80 km) from the center of circulation.  Winds to tropical storm force extend out more than 200 miles (320 km) from the center.  The Hurricane Intensity Index (HII) for Typhoon Megi is 17.8.  The Hurricane Size Index (HSI) is 18.7 and the Hurricane Wind Intensity Size Index (HWISI) is 36.5.

The circulation of Typhoon Megi is very symmetrical.  Numerous bands of thunderstorms are rotating around the center.  A circular eye appears to be forming at the center of circulation.  Thunderstorms near the center and in the rainbands are generating upper level divergence which is pumping out large quantities of mass in all directions.

Typhoon Megi is moving through a very favorable environment.  It is moving over water where the Sea Surface Temperature is near 30°C.  The upper level winds are weak and there is little vertical wind shear.  Typhoon Megi is likely to continue to intensify and it could become the equivalent of a major hurricane on Sunday.

Typhoon Megi is moving southwest of a subtropical ridge which is steering it toward the west-northwest and that general motion is expected to continue for several more days.  On its anticipated track Typhoon Megi will approach Taiwan in about 48 hours.

Typhoon Megi is large and dangerous typhoon.  It is likely to bring strong winds and heavy rain to Taiwan.

Tropical Storm Karl Approaching Bermuda

Tropical Storm Karl continued to move steadily toward Bermuda on Friday.  At 5:00 p.m. EDT on Friday the center of Tropical Storm Karl was located at latitude 29.9°N and longitude 65.1°W which put it about 165 miles (270 km) south of Bermuda.  Karl was moving toward the north at 13 m.p.h. (20 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.

A Hurricane Watch has been issued for Bermuda.  A Tropical Storm Warning is also in effect for Bemruda.

Tropical Storm Karl strengthened on Friday, but its structure remained asymmetrical.  Almost all of the thunderstorms are in a primary rainband that wraps around the northern and western sides of the center of circulation.  There are few if any thunderstorms south and east of the center.  It appears as it vertical wind shear is tilting the circulation toward the northwest.  The upper level center appears to be located 20 to 30 miles (30 to 50 km) northwest of the low level center.  The thunderstorms in the primary rainband are producing upper level divergence which is pumping out mass to the east of Tropical Storm Karl.  The upper level divergence pumped out enough mass on Friday to allow the surface pressure to decrease by about 10 mb.  However, the vertical wind shear and lack of thunderstorms to the east of the center limited the increase in wind speed at the surface.

Tropical Storm Karl is moving over water where the Sea Surface Temperature is near 29°C.  So, there is enough energy in the upper ocean to support a stronger storm.  However, an upper level trough to the west of Karl is creating significant vertical wind shear, which is likely to limit intensification in the short term.  When Tropical Storm Karl, turns east and moves farther from the upper level trough, the shear could decrease and Karl could strengthen.  In addition Karl will begin a transition to an extratropical cyclone and that transition often produces and increase in the wind speed.  So, Tropical Storm Karl does have a chance to become a hurricane during the weekend.

Tropical Storm Karl is moving around the western end of a subtropical ridge which is steering it toward the north.  It is likely to keep moving in that direction for another six to twelve hours.  When Tropical Storm Karl nears Bermuda it will encounter stronger westerly winds which will turn it eastward.  Karl is likely to move quickly toward the east-northeast on Saturday and Sunday.  On its anticipated track Tropical Storm Karl will pass near Bermuda on Saturday morning.  It will bring a period of gusty winds and heavy rain.

Tropical Storm Megi Forms West of the Marianas

Tropical Storm Megi formed west of the Marianas on Friday.  At 11:00 a.m. EDT on Friday the center of Tropical Storm Megi was located at latitude 16.4°N and longitude 137.1°E which put it about 1160 miles (1870 km) east-southeast of Taipei, Taiwan.  Megi was moving toward the west at 15 m.p.h. (24 km/h).  The maximum sustained wind speed was 45 m.p.h. (70 km/h) and there were wind gusts to 60 m.p.h. (95 km/).  The minimum surface pressure was 996 mb.

The circulation of Tropical Storm Megi is still organizing.  A distinct center of circulation is still consolidating.  There are more thunderstorms south and east of the center of circulation, but bands of thunderstorms are beginning to develop in other quadrants of the storm.  The thunderstorms closer to the center are generating upper level divergence which is pumping out mass.  Outflow channels could be developing to the northwest and southeast of Tropical Storm Megi.

Tropical Storm Megi is moving into an environment that is favorable for intensification.  It 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.  Tropical Storm Megi is likely to continue to intensify while the circulation becomes better organized.  Once a well formed core develops at the center of Megi, it could intensify more rapidly.  Tropical Storm Megi is likely to become a typhoon during the weekend.

Tropical Storm Megi is moving along the southwestern side of a subtropical ridge, which is steering it toward the west.  A westerly or west-northwesterly motion is expected to continue for the next few days.  On its anticipated track Tropical Storm Megi could approach Taiwan in about three days.  Megi is likely to be a typhoon at that time.