Atlantic Tropical Weather Update 9/10/09

Sorry for the break in posts.  A technical workshop was on tap at work this week and preparations had to be made.  All that is over, so I expect to return to a more regular posting frequency.

The Atlantic hasn’t kept quiet this week.  The tropical wave I noted in my last Update was vigorous enough to develop into a Tropical Depression, Tropical Storm, Hurricane and Major Hurricane in the past two and a half days.  That’s pretty impressive.  During that time, Fred moved around to the south and west of the Cape Verde Islands, where he resides now.  Here are Hurricane Fred’s vitals as of this evening:

Center located at 17.3N, 35.1W; moving N @ 5mph; maximum sustained winds of 90mph.

Those wind speeds were enough to make Fred a major hurricane, as I noted above.  At peak strength, Fred packed 105mph winds and had a minimum central pressure below 975mb.

So thus far in the Atlantic basin, we’ve seen one Tropical Depression, 4 Tropical Storms and 2 Major Hurricanes.  It is worth noting that both Hurricane Bill and Fred were Cape Verde Storms.  Fred intensified a large distance to the southeast that Bill did, but both strengthened out in the middle of nowhere.  In contrast, all of the Tropical Storms have formed much further west and for one reason or another, never managed to organize themselves enough to become hurricanes.

Hurricane Fred has dredged up a large volume of colder water as he ingested the warm surface waters off the Cape Verde Islands.  That should, all other things being equal, prevent another tropical wave from developing in the same area for a couple of weeks, regardless of the wave’s intensity coming off from Africa.

Hurricane Fred is forecasted to stall over the next few days, slowly losing strength as he does so.  He is moving in reaction to an upper-level trough moving from west to east to Fred’s north.  Once it passes and the subtropical ridge builds back in, Fred should move off to the west again.  At that time, he is currently expected to be a remnant low with little chance of redevelopment.

Atlantic Tropical Weather Update 9/4/09

Tropical Storm Erika decayed to a Tropical Depression yesterday and a remnant low today.  The center of circulation became detached from the convective thunderstorms, necessitating the change in status.  The thunderstorms continue to move west across the northeast Caribbean Sea.  There is a <30% chance of redevelopment in the next couple of days with the disturbance.

Much further east across the Atlantic Ocean, the tropical wave that moved from Africa to the Atlantic continues to look impressive.  The NHC has designated this disturbance as having a 30-50% chance of tropical development within the next 48 hours.  It consists of a broad region of relatively low pressure and some thunderstorms.  A good amount of organization will have to occur before it becomes a Tropical Depression.

Atlantic Tropical Weather Update 9/2/09

There has been a small but fairly significant change to Tropical Storm Erika’s forecast.  But let’s start with her vitals:

Center located at 16.5N, 60.4W; moving W @ 10mph; maximum sustained winds of 40mph; minimum central pressure of 1008mb.

Tropical Storm Erika’s center location is just offshore a few of the northeast Windward Islands: Guadeloupe and Antigua are closest to her circulation.  That positioning is well to the west of where she was yesterday.  As such, the track forecast envelope that a suite of models has come up with is similarly shifted.  That, of course, has implications throughout the next five days.

Tropical Storm Erika’s official track forecast continues to brush the storm against numerous islands over the next couple of days.  Antigua, Montserrat, Barbuda, Saint Martin, Saint Croix, and Saint Thomas are all in or near the expected path of this Tropical Storm.  Thereafter, T.S. Erika should pass to the northeast of San Juan, Puerto Rico Friday morning.  It is expected to continue moving northwest through Sunday, which would take the storm to the north of Hispanola, but over the Turks and Caicos Islands of the Bahamas.  Between Sunday and Monday, the official track forecast shifts the storm’s movement more to the NNW, keeping it to the east of other Bahama Islands.  That will likely take place Monday, all of which would be irrelevant if there is any short-term change to Erika’s path.

It should be noted that the official track forecast is on the northern portion of the model solution envelope.  Many models take Erika over Puerto Rico and Hispanola.  Interestingly, one model threads Erika by a series of islands, including between Cuba and Florida in the extended forecast.  I don’t buy this solution over any other – it’s just interesting.

The official intensity forecast is also interesting.  By Day 4, the NHC is calling for the storm to fall below Tropical Storm strength and continue along as a Tropical Depression instead.  This is because of the unexpected appearance of strong shear at upper-levels, which is making it difficult for Erika to establish outflow of rising air.  Compare this case to that of Bill, which developed excellent outflow early on, helping the system to intensify quickly.  A lot of factors have to come together at the same time for these systems to remain organized and intensify.

Elsewhere, the tropical wave that exited Africa over the weekend has dissipated.  No organized convection can currently be found where the disturbance was.  The next tropical wave transiting Africa is preparing to enter the far eastern Atlantic over the next day.  This wave is very vigorous – whether this continues over the ocean remains to be seen.  There is plenty of moist air surrounding this disturbance, but a rather intense shear environment is just to the disturbance’s north.

Atlantic Tropical Weather Update 9/1/09

[Update 3:00P MDT]: Tropical Storm Erika has formed.

The NHC had hurricane hunter aircraft investigate the tropical disturbance known as Invest-94 this afternoon.  They have reported that a broad-scale, but closed circulation was found.  Directly sampling the environment, they found sustained wind speeds of 50mph near the “center”.  This means the storm is a Tropical Storm.  The difficulty of ascertaining the storms’ characteristics from satellite data isn’t new – remote sensing will always have its disadvantages to go along with its advantages.

Tropical Storm Erika’s vitals are as follows: center located near 17.2N, 57.3W; moving WNW @ 9mph; maximum sustained winds of 50mph; minimum central pressure of 1007mb.

There isn’t any change in the official track forecast – it takes the storm to the north of the northeast Caribbean Islands the next few days.

Tropical Storm Erika should continue to be a Tropical Storm over the next few days as it fights some wind shear on the western side of the storm.

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Invest-94 stubbornly refuses to get enough organization and structure to be classified as a Tropical Depression or Storm.  Meanwhile, it draws closer to land forms in the western Atlantic Ocean.  Here is Invest-94′s vitals as of this morning:

“Center” located near 16.8N, 57.2W; moving WNW @ 9mph.

The tropical disturbance has gone through fits and starts of rather impressive thunderstorm development, but has suffered from a lack of a well-defined closed-off low pressure center.  Some mid-level shear influences are currently thought to be the cause of the lack of organization.

The official track forecast, such as it is, takes Invest-94 to the north of the Caribbean Islands, such as the northern Windward Islands, Puerto Rico and Hispanola.  A wide spread in final position still exists for Days 4 and 5, when the system could be anywhere from north of the Bahamas on it way toward the Carolinas to just north of Hispanola, steering towards the southeastern Bahama Islands.

The official intensity forecast is as muddled as the track forecast.  Models continue to call for intensification, which hasn’t happened the past three or four days when the models were very excited about developing the storm.  Hurricane hunter aircraft are on the way today, and should shed more light on local storm conditions and help pin down exactly what’s spinning over the ocean.

The tropical wave that exited Africa yesterday is centered just east of the Cape Verde Islands.  The NHC has labeled the area of disturbed weather as an area of interest, giving it <30% chance of tropical development in the next 48 hours.

So, a temporary lull in tropical activity in the Atlantic exists while Category 4 Hurricane Jimena bears down on the Mexican Baja peninsula.  Hopefully damage and lives lost are kept to a minimum there.

Atlantic Tropical Weather Update 8/31/09

Invest-94 continues to exhibit increasing organization today, while the banded cloud features are only moderately impressive.  The system still doesn’t have a dominant central low pressure center.  This disturbance is definitely still a tropical wave, not yet a tropical depression.

Invest-94′s general center of circulation is located near 15.6N, 53.4W (~500 miles east of the Windward Islands) ; is moving WNW @ 14mph; and has maximum sustained winds of 30mph.

The disturbance’s movement in the past 12+ hours has taken it more northerly than I thought it would last night.  It should continue its WNW/NW movement throughout the next day or so.  After that, there is considerable divergence of model track solutions.  The NOGAPS keeps moving the storm NW, while the GFS, LBAR and BAMM shift its track to almost due west after Day 2.  The HWRF comes up with a snaking pattern: WNW, W, then WNW again in days 4-5.  The multitudes of track solutions means that anything from no impact on islands is possible, as is a glancing blow to the northern Windward Islands, Puerto Rico and Hispanola.

Continued organization and intensification is also progged by models, but this was the case all day yesterday as well.  The only thing to take from this is that intensification to Tropical Depression status is likely in the next day or so.  SSTs are plenty warm and the system will encounter less wind shear as it continues to travel across the basin.

Much further east, another tropical wave is exiting Africa over the Atlantic.  This wave is fairly far north – about 12.5N or so.  It isn’t that vigorous either.  A wave still over Africa looks a little better on satellite imagery.  It will be many days before either of these disturbances make their mark on the Atlantic basin, if at all.

Atlantic Tropical Weather Update 8/30/09

The Atlantic hurricane season is in medium- to high-gear.  While Tropical Depression Danny was being absorbed by a synoptic low moving off the U.S. coast, a vigorous tropical wave has been moving west across the Atlantic basin.  This wave has slowly grown more organized as it has made its trek westward.

At this time, Invest-94 is located 850 miles east of the Windward Islands.  It loosely looks like a tropical storm with the stirrings of potential rain bands moving around a central low pressure site.

Invest-94′s center is located near 12.6N, 48.3W; is moving WNW @ 11mph; and has maximum sustained winds of 30mph.

Invest-94 should continue moving WNW or NW over the next few days.  This expected path would put it near the northern Windward Islands in two to three days.  It has the potential to impact Puerto Rico in days 4-5.  It could also just as well steer north of the islands and remain over the Atlantic, like Bill did earlier this season.

Invest-94 is forecasted to continue to organize and strengthen over the next 3-5 days, becoming a tropical depression in the next day, a tropical storm a day or so after that and even a hurricane in the last part of the forecast period.  Water temperatures are more than warm enough to sustain a hurricane – over 28C waters now, 29C waters in days 2-5.  Wind shear is expected to remain minimal over the next few days, so Invest-94 should have nothing in its way to prevent it from strengthening.

Atlantic Tropical Weather Update 8/27/09

The fourth named storm of the 2009 Atlantic Hurricane Season has formed – Tropical Storm Danny was a tropical wave that had made it north of the Caribbean Islands and interacted with an upper-level low.  Enough organization occurred to allow the storm to be named.  Here are Tropical Storm Danny’s vitals as of this morning:

Center located at 27.4N, 72.1W; moving NW @ 10mph; maximum sustained winds of 60mph; minimum central pressure of 1006mb.

Tropical Storm Danny’s official track forecast is a near duplicate of Hurricane Bill’s.  He is moving around the western periphery of the sub-tropical ridge over the mid-Atlantic.  His course should take him by the east coast of the U.S., but no landfall should occur there.  Instead, T.S. Danny is expected to come ashore either over New Brunswick or Nova Scotia.  It will be a couple of more days before that final landfall area becomes more clear.

Tropical Storm Danny’s official intensity forecast intensifies him to a hurricane by Saturday morning.  He should maintain that strength through the weekend, affecting the Canadian maritimes as a Category 1 storm.

Elsewhere, Invest 94 emerged over the Atlantic early yesterday.  It is moving west across the Atlantic basin.  It is currently south-southwest of the Cape Verde Islands.  It consists mostly of disorganized thunderstorms at this time, though this might change in the next couple of days.  This system might stay to the south of where Hurricane Bill and Tropical Storm Danny moved.  If that happens, it would pass over the Windward Islands in six days.

Atlantic Tropical Weather Update 8/18/09 #3

The first major hurricane of the 2009 Atlantic season is Hurricane Bill.  Here are his vitals as of tonight:

Center located at 17.2N, 53.4W; moving WNW @ 14mph; maximum sustained winds of 125mph; minimum central pressure of 952mb, which is a drop of ~10mb since earlier this afternoon.

The drop in central pressure means that further strengthening is likely for Hurricane Bill.  He is a strong Category-3 storm right now.  The threshold between Category-3 and Category-4 storms is 130mph.  As such, the NHC has revised its official intensification forecast: by tomorow morning at 8A EDT, Hurricane Bill should be a Category-4 storm.  That condition is likely to last through Friday, with cyclical weakening and strengthening as the storm begins to replace eye-walls.

The official track forecast takes Hurricane Bill north of 30N by late Friday night, meaning Bermuda is in for a rough Saturday morning.  Given the relatively high latitude, decreasing ocean heat content and increasing wind shear, Hurricane Bill should begin to permanently weaken after Friday night.  By Saturday night, Bill is forecasted to be due east of North Carolina as a Category-3 storm.  By Sunday night, Bill is now forecasted to be due south of Nova Scotia, Canada as a Category-2 storm.  Thereafter, Bill is likely to keep decaying and taking on extra-tropical characteristics.

Some ensemble model solutions take Bill ashore near Connecticut.  Others take him ashore on New Brunswick, Nova Scotia or far-east Quebec.  All of them take Bill across the north Atlantic before possibly impacting the British Isles next week.  The landings near CT, NB, NS or Quebec are unlikely solutions.  They are possible, however, so the storm should remain in folks’ interest until it has passed you by.

Tropical Weather Update 8/18/09 #2

There is a status update on Hurricane Bill.  His vitals as of this afternoon:

Center located at 16.6N, 52.2W; moving WNW @ 16mph; maximum sustained winds of 110mph; minimum central pressure of 962mb.

Those winds mean Hurricane Bill is a borderline Category2/Category3 storm.  At this point, this difference boils down to semantics.  111mph sustained winds are the threshold for a Category 3 storm.  The practical difference between 110mph and 111mph winds?  Negligible at best.

The NHC continues to forecast an upgrade to Category 3 statues by 2AM tomorrow morning EDT.  They should designate it as a Cat-3 this afternoon; tonight at the latest.

The official intensity forecast has been updated as a result.  Hurricane Bill is now forecasted to become a Category-4 storm by this time tomorrow.  That’s an impressive acknowledgment of a favorable storm environment and a robust storm taking advantage of its environment.  All the intensity models forecast a continuation in intensification through the next 36-48 hours, after which a gradual but persistent weakening should occur through the end of the forecast period.

Atlantic Tropical Weather Update 8/18/09 #1

The remnants of Tropical Storm/Depression Claudette are slowly making their way up through the southeastern U.S.  There are actually as many showers to her south due to typical August diurnal heating.

The remnants of Tropical Storm/Depression Ana continue to move west across the Bahamas and Cuba.  They are interacting with another upper-level disturbance, which is helping to produce widespread rain showers over the area.  No tropical development of this system is likely in the next day or two.

That leaves Hurricane Bill.  Here are his vitals as of this morning:

Center located at 15.9N, 51.2W (719 miles E of Guadeloupe); moving WNW @ 16mph; maximum sustained winds of 105mph; minimum central pressure of 963mb.

The 105mph winds and 963mb pressure makes Bill a strong Category 2 hurricane.  To become a Category 3 (major hurricane), the winds need to be sustained at 111-130mph.  The satellite imagery on Bill continues to look impressive with a well-defined eye-wall and large spiral bands.

Hurricane Bill’s official track forecast pushes Bill toward the NW starting tomorrow, then NNW Friday, then NNE Saturday.  All the model solutions are in agreement with this general track pattern with only slight differences between them.  This path takes Bill over Bermuda on Saturday.

Hurricane Bill’s official intensity forecast makes Bill a Category 3 storm between 8PM EDT tonight and 8AM EDT tomorrow morning.  A series of hurricane hunter missions are being launched to investigate Bill starting today – they will be able to provide much better detailed storm information than what have been available thus far.  Surface-level wind and pressure readings will be more accurate soon.  It’s that information that I want to see – hopefully the flight returns data right after Bill intensifies to Category 3 strength.

The 2nd tropical wave behind Bill is still entering the Atlantic.  This wave isn’t as impressive as Bill was at the same juncture.  As of now, the NHC doesn’t have an area of interest on the system like it did for Bill.