Monthly Archives: June 2017

Invests 92L, 93L Monitored for Possible Development

Two weather systems designated as Invest 92L and Invest 93L are being monitored for possible development into tropical cyclones.  Invest 92L is a tropical wave that is speeding toward the Windward Islands.  At 2:00 p.m. EDT on Sunday the center of Invest 92L was located at latitude 7.3°N and longitude 49.4°W which put it about 800 miles (1290 km) east-southeast of the Windward Islands.  It was moving toward the west-northwest at 24 m.p.h. (39 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. (75 km/h).  The minimum surface pressure was 1008 mb.

Invest 93L consists of a broad area of low pressure over the northwestern Caribbean Sea.  At 2:00 p.m. EDT on Sunday the surface center of Invest 93L was located at latitude 19.0°N and longitude 87.1°W which put it about 145 miles (230 km) south of Cancun, Mexico.  It was moving toward the north-northwest at 5 m.p.h. (8 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 1006 mb.

Invest 92L is a tropical wave and it has not yet develop a well defined surface center.  There is some evidence of cyclonic rotation on visible satellite imagery and there could be a center in the middle levels of the circulation.  Most of the stronger thunderstorms are located north and west of the center.  The are some bands of showers and thunderstorms south and west of the center.  There is some upper level divergence from the thunderstorms north and west of the center, but it is not well developed at the current time.

Invest 92L is in an environment that is moderately favorable to development of a tropical cyclone.  It is moving over water where the Sea Surface Temperature is near 28°C.  It is in a region of rapid easterly flow, but the wind speed is fairly similar at all levels.  So, there is not a lot of vertical wind shear.  The rapid easterly flow could be inhibiting the formation of a well defined center of circulation.  Invest 92L will be in a moderately favorable environment for about another 36 hours.  An upper level trough over the eastern Caribbean Sea will create increased vertical wind shear when Invest 92L reaches that location.  The National Hurricane Center is indicating that there is a 60% probability that Invest 92L will develop into a tropical cyclone during the next two days.

Invest 92L is being steered rapidly toward the west-northwest by a subtropical high north of it.  A fairly quick motion toward the west-northwest is expected to continue for the next few days.  On its anticipated track Invest 92L could be near the Windward Islands by late Monday.  Even it if does not develop into a tropical cyclone, the system will bring gusty winds and locally heavy rain to those islands.

The structure of Invest 93L is much more complicated.  There is a very broad but weak surface low pressure system over the Yucatan peninsula and the center of that low is being used as the center of the Invest.  However, there is a strong mid-level center of circulation near latitude 18.7°N and longitude 82.9°W which is about 115 miles (185 km) west-southwest of Grand Cayman.  Invest 93L is producing winds to near tropical storm force and those winds are occurring in thunderstorms associated with the mid-level circulation.  It is possible that downdrafts in those thunderstorms could transport enough momentum to the surface to generate a new surface center beneath the mid-level center.

Invest 93L is moving in an environment that will be favorable for the development of a tropical cyclone.  An upper level ridge is building between the trough over the eastern Caribbean Sea and another upper level trough over the northwestern Gulf of Mexico.  The trough over the northwestern Gulf is producing strong southwesterly winds which are causing vertical wind shear over the surface low over the Yucatan peninsula.  However, the upper level ridge is producing an area of slower winds over the mid-level center and there is less vertical wind shear there.  In fact, the upper level ridge is enhancing upper level divergence over the mid-level center.  If that continues, surfaces pressure will begin to decrease in that region.  The National Hurricane is indicating that there is a 70% probability of development of a tropical cyclone or a subtropical cyclone during the next two days.

Invest 93L is moving slowly north-northwestward around the western end of the subtropical high over the Atlantic Ocean.  A general north-northwesterly motion is expected to continue for another day or two, but there is some spread in the guidance from the numerical models.  If a cyclone forms from the surface low over the Yucatan peninsula, then the greatest risk would be to the western Gulf of Mexico.  If a new surface center forms farther east under the mid-level center, then there would be a greater risk for the central and eastern Gulf of Mexico.  Interests around the Gulf should monitor Invest 93L.

Two Areas to Watch for Potential Tropical Development

There are two areas to watch for the potential development of a tropical cyclone during the next week.  One location to watch for potential development is the area around the western Caribbean Sea, Yucatan peninsula and southern Gulf of Mexico.  The other area to watch is the tropical Atlantic between Africa and the Lesser Antilles.

Numerical models have been suggesting possible development of an area of low pressure somewhere over the western Caribbean Sea, Yucatan peninsula or southern Gulf of Mexico.  The scenario suggested by the models includes a surge of southerly winds across Central America, which contributes to the spinning up of an area of low pressure.  There are currently strong westerly winds in the upper levels over this area.  The strong vertical wind shear will prevent development of a tropical cyclone in the short term.  An upper level ridge could develop over the area in several days.  If that happens, the wind shear would decrease.  Some runs of the numerical models create a broad, weak area of low pressure, which would primarily be a rain threat for the Yucatan peninsula and nearby regions.  Other models develop a low pressure system that is a little stronger, although those lows also weaken when they move over the Yucatan.  The models generally move the low pressure system northwestward over the southern Gulf of Mexico.  However, there are fairly significant deviations in how far north the low moves once it is in the Gulf.  As of 8:00 p.m. EDT on June 14 the National Hurricane Center was indicating that there was a 30% probability of the development of a tropical cyclone in this area during the next five days.

Some numerical models have also been suggesting potential development of a tropical cyclone near latitude 10°N over the tropical Atlantic Ocean between Africa and the Lesser Antilles.  A tropical wave is interacting with the Intertropical Convergence Zone and there has been a persistent area of showers and thunderstorms.  The disturbance is moving slowly toward the west.  There is some vertical wind shear in this region, but the stronger upper level winds are north of the disturbance.  The disturbance is over water where the Sea Surface Temperature is near 27°C.  It would be unusual to see a tropical cyclone develop over the tropical Atlantic in June, but it has happened at least three times in the past.  As of 8:00 p.m. EDT on June 14 the National Hurricane Center is indicating that there is a 20% probability of the development of a tropical cyclone in this region during the next five days.

TD 03E Strengthens Into Tropical Storm Calvin

Tropical Depression 03E strengthened into Tropical Storm Calvin on Monday as it lingered south of Mexico.  At 5:00 p.m. EDT on Monday the center of Tropical Storm Calvin was located at latitude 15.5°N and longitude 95.5°W which put it about 70 miles (110 km) east-southeast of Puerto Angel, Mexico.  Calvin was moving toward the west-northwest at 2 m.p.h. (3 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 1005 mb.  A Tropical Storm Warning remains in effect for the portion of the coast from Boca De Pijijiapan to Punta Maldonado.

A band of thunderstorms wrapped tightly around the southern side of the center of circulation of former Tropical Depression 03E and the National Hurricane Center upgraded the system to Tropical Storm Calvin in its 5:00 p.m. EDT advisory on Monday.  Calvin is a small tropical storm and winds to tropical storm force only extend out about 60 miles (95 km) from the center of circulation.  Additional bands of showers and thunderstorms are occurring in the outer portions of the circulation which are over the Pacific Ocean.

Tropical Storm Calvin is in an environment that is marginally favorable for intensification.  It is over water where the Sea Surface Temperature is near 30°C.  However, Calvin is also very near the coast of Mexico and it could start to pull drier air into the western part of the circulation at any time.  Calvin is under the eastern end of an upper level ridge which is producing northerly winds which are blowing toward the top of the tropical storm.  The northerly winds are producing moderate vertical wind shear and the shear may be contributing to the location of the main band thunderstorms south of the center of circulation.

The future intensity of Tropical Storm Calvin will depend on whether or not it remains over the Pacific Ocean.  If Calvin stays over the open water, then further intensification is possible.  If Calvin moves closer to the coast, then further intensification is much less likely.  If Calvin moves inland, it will dissipate quickly.

Tropical Storm Calvin is in an area where the steering currents are weak and it moved very slowly toward the west-northwest during the past 18 hours.  A subtropical ridge north of Calvin is forecast to begin to steer the tropical storm more quickly toward the west-northwest.  If that happens, Calvin could make landfall on the coast of Mexico near Puerto Angel in 12 to 24 hours.  Locally heavy rainfall remain the biggest risks with Tropical Storm Calvin.

Tropical Storm Merbok Makes Landfall Near Hong Kong

Tropical Storm Merbok made landfall near Hong Kong on Monday.  At 5:00 p.m. EDT on Monday the center of Tropical Storm Merbok was located at latitude 23.5°N and longitude 114.9°E which put it about 55 miles (85 km) north-northeast of Hong Kong.  Merbok was moving toward the north at 11 m.p.h. (17 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1005 mb.

Tropical Storm Merbok intensified before it made landfall and the maximum sustained wind speed was around 55 m.p.h. (85 km/h) at the time of landfall.  Merbok began to weaken after landfall and the strongest winds are now occurring in bands over the the open water.  Merbok is producing locally heavy rain in bands east of the center if circulation.  The heavy rains represent the greatest risk and flooding is possible over parts of eastern China.  Merbok is a fairly small tropical storm and the heavier rain will fall primarily to the east of the track of Merbok.  Merbok should gradually spin down as it moves farther inland.

Formation of Tropical Depression 03E Prompts Mexico to Issue Warning for Coast

Tropical Depression 03E formed out of the cluster of thunderstorms formerly known as Invest 92E and the government of Mexico issued a Tropical Storm Warning for a portion of the south coast.  At 5:00 p.m. EDT on Sunday the center of Tropical Depression 03E was located at latitude 14.5°N and longitude 95.0°W which put it about 105 miles (170 km) southeast of Puerto Angel, Mexico.  The depression was moving toward the northwest at 5 m.p.h. (7 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. (75 km/h).  The minimum surface pressure was 1007 mb.  A Tropical Storm Warning is in effect for the portion of the coast from Boca De Pijijiapan to Punta Maldonado, Mexico.

A distinct center of circulation developed within an area of thunderstorms that had been lingering over the Eastern North Pacific Ocean south of Mexico.  More thunderstorms formed closer to the center of circulation and the National  Hurricane Center determined that there was sufficient organization to designate the system as Tropical Depression 03E.  The stronger thunderstorms were occurring in a partial band close to the center of circulation.  Additional bands of showers and thunderstorms were forming in bands in other parts of the circulation.  The thunderstorms near the center have not yet begun to generate significant upper level divergence.

Tropical Depression 03E will be moving through an environment that is marginally favorable for intensification.  The depression will move over water where the Sea Surface Temperature is near 30°C.  It is moving under the western end of an upper level ridge.  The ridge is generating southeasterly winds which are blowing toward the top of the circulation.  Those winds are generating moderate vertical wind shear which is restricting upper level divergence to the east of the circulation.  The shear is inhibiting intensification.  Tropical Depression 03E will probably be able to extract enough energy to intensify into a tropical storm.

Tropical Depression 03E is moving around the western end of a subtropical ridge which is steering it toward the northwest.  A generally northwesterly motion is forecast for the next 24 to 48 hours.  On its anticipated track Tropical Depression 03E could approach the southern coast of Mexico in 24 to 36 hours.  It could be a tropical storm by that time.  Tropical Depression 03E is likely to bring gusty winds, locally heavy rain and the potential for flash floods to parts of southern Mexico.

Tropical Storm Merbok Moves Closer to China

Tropical Depression 04W intensified into Tropical Storm Merbok on Sunday as it moved closer to the coast of China.  At 5:00 p.m. EDT on Sunday the center of Tropical Storm Merbok was located at latitude 19.9°N and longitude 115.7°E which put it about 220 miles (360 km) south-southeast of Hong Kong.  Merbok was moving toward the north-northwest at 16 m.p.h. (26 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 999 mb.

The structure of Tropical Storm Merbok is asymmetrical.  Most of the thunderstorms are occurring east and south of the center of circulation.  A primary rainband curves about halfway around the southeastern side of the center.  Additional bands of showers and thunderstorms exist outside the core in southeastern half of Merbok.  There are bands in the northwestern half of the circulation but they consists primarily of low clouds and showers.  The thunderstorms in the primary rainband are producing upper level divergence which is pumping out mass to the south of Tropical Storm Merbok.

Tropical Storm Merbok is moving through an environment that is marginally favorable for intensification.  It is moving over water where the Sea Surface Temperature is near 29°C.  Merbok is moving under the eastern end of an upper level ridge which is producing northerly winds which are blowing toward the top of the tropical storm.  Those northerly winds are creating moderate vertical wind shear, but they are also enhancing the upper level divergence to the south of Merbok.  Tropical Storm Merbok appears to be pulling some drier air from China into the northwestern part of the circulation.  The combination of moderate vertical wind shear and drier air could be the reason for the asymmetrical distribution of thunderstorms.

Tropical Storm Merbok has a chance to intensify a little more before it makes landfall.  The effects of the moderate vertical wind shear and drier air should limit any intensification and Merbok is likely to remain a tropical storm until it makes landfall.

Merbok is moving around the western end of a subtropical ridge which is steering the tropical storm toward the north-northwest.  That general motion is expected to continue for another day or so.  On its anticipated track the center of Tropical Storm Merbok will reach the coast of China between Hong Kong and Shantou in 12 to 18 hours.  Tropical Storm Merbok will bring gust winds and locally heavy rain.  When Merbok moves inland over eastern China, it will reach the westerly winds in the middle latitudes and those winds will turn the tropical storm toward the east.

Tropical Depression 04W Forms West of Luzon

Tropical Depression 04W formed west of Luzon on Saturday.  At 11:00 p.m. EDT on Saturday the center of Tropical Depression 04W was located at latitude 16.6°N and longitude 116.8°E which put it about 430 miles (690 km) south-southeast of Hong Kong.  The depression was moving toward the northwest at 10 m.p.h. (16 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. (75 km/h).  The minimum surface pressure was 1006 mb.

An area of thunderstorms moved west-northwestward across the Philippines and a circulation slowly consolidated around a distinct center.  The center of circulation became well enough defined on Saturday to cause the system to be classified as Tropical Depression 04W.  The inner core of the depression is still organizing.  A band of thunderstorms wrapped around the western and southern sides of the center of circulation.  Additional bands of showers and thunderstorms developed in other parts of the depression.  The area of showers and thunderstorms southwest of the center began to generate upper level divergence which pumped mass away from the depression.

Tropical Depression 04W will be moving through an environment that is favorable for intensification.  The depression will move over water where the Sea Surface Temperature is near 30°C.  The depression is moving under the eastern end of an upper level ridge.  The ridge is producing northerly winds which are blowing toward the top of the circulation.  The vertical wind shear may be part of the reason why there are more thunderstorms south of the center of circulation, but the shear is not strong enough to prevent intensification.  Tropical Depression 04W is expected to intensify into a tropical storm during the next 24 hours.

Tropical Depression 04W is moving around the western end of a subtropical ridge which is steering it toward the northwest.  A general northwesterly motion is expected for another 36 to 48 hours.  A turn toward the east will occur after that time.  On its anticipated track Tropical Depression 04W could be near Hong Kong in about 36 hours.  Tropical Depression 04W will have strengthened into a tropical storm by that time and there is a chance it could intensify into a typhoon by the time it nears the coast of China.

Tropical Storm Beatriz Brings Heavy Rain to Southern Mexico

Tropical Depression Two-E intensified into Tropical Storm Beatriz on Thursday and Beatriz brought heavy rain to parts of southern Mexico.  At 5:00 p.m. EDT on Thursday the center of Tropical Storm Beatriz was located at latitude 15.5°N and longitude 96.8°W which put it about 25 miles (40 km) southwest of Puerto Angel, Mexico.  Beatriz was moving toward the north-northeast at 5 m.p.h. (8 km/h).  The maximum sustained wind speed was 45 m.p.h. (75 km/h) and there were wind gusts to 60 m.p.h. (95 km/h).  The minimum surface pressure was 1004 mb.  A Tropical Storm Warning was in effect for the portion of the coast from Salina Cruz to Puerto Escondido.

Tropical Depression Two-E intensified into Tropical Storm Beatriz on Thursday even though its structure evolved into a more asymmetrical system.  Tropical Storm Beatriz appeared to consist of a larger low pressure system which was centered just off the coast of Mexico.  The weather radar from Puerto Angel confirmed that the center of circulation was still offshore.  There were several smaller (mesoscale) counterclockwise rotating circulations that were revolving around the center of the larger low.  At least one of the smaller circulations was already over southern Mexico.  Many of the thunderstorms were occurring in a broad band that wrapped around the eastern and northern portions of the larger low pressure system.  The strongest winds were occurring within this primary rainband.  There were far fewer thunderstorms in the western half of the circulation.  It seemed that after air descended from mountains in Mexico then the air was drawn into the western side of Tropical Storm Beatriz.  The warmer drier air was inhibiting the formation of thunderstorms in the western half of Beatriz.

Although Tropical Storm Beatriz is over water where the Sea Surface Temperature is near 30°C, other environmental factors are unfavorable for intensification.  The proximity to land and the apparent ingestion of drier air are both negative factors.  A narrow upper level ridge oriented from the south-southwest to the north-northeast and a upper level trough to the west of Beatriz are producing brisk southerly winds that are blowing toward the top of the circulation.  Those upper level winds are causing moderate vertical wind shear.  Therefore, Tropical Storm Beatriz is unlike to intensify further during the next several days.

The future track of Tropical Storm Beatriz is uncertain.  If the circulation of Beatriz remains intact then the upper level trough and upper level ridge are likely to steer it toward the north-northeast.  Tropical Storm Beatriz would dissipate over the mountains of Mexico if that scenario occurs.  If the upper level winds are strong enough, the vertical shear could detach the upper portion of the circulation from the low level circulation.  That scenario sometimes occurs when slow moving storms approach the south coast of Mexico.  If that happens, the upper half of the circulation could be transported across Mexico and move over the southern Gulf of Mexico.  Some models are suggesting that a new surface low could form over the southern Gulf in several days, but the wind shear would have to decrease in order for that to occur.  The lower level circulation could be left behind near the coast of Mexico where it would drift slowly near the coast.

Tropical Storm Beatriz is bringing heavy rains to parts of southern Mexico and the heavy rain will continue to fall on Friday.  Locally heavy rain in the more mountainous portions of Oaxaca could create the potential for dangerous flash floods.