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.

Atlantic Tropical Weather Update 8/17/09 #3

Things in the Atlantic are temporarily winding down as fast as they were wound up.  Tropical Storm Claudette made landfall over the panhandle of Florida this morning.  Tropical Depression Ana has totally decayed and is just a broad area of lower surface pressures and scattered thunderstorms over the Atlantic.

Hurricane Bill remains the only game in town for the moment.  Here are his vitals tonight:

Center located at 15N, 48.3W; moving WNW @ 17mph; maximum sustained winds of 100mph; minimum central pressure of 967mb.

The 100mph/967mb readings mean Bill is a solid Category 2 Hurricane tonight.  His pressure reading decreased throughout the day, so further strengthening is likely tomorrow – Bill should become the first major hurricane of the 2009 season.

Bill looks outstanding on satellite imagery – a classic-looking hurricane with strong outflow to all quadrants, spiral bands and a developing eye-wall visible from space.

The official track forecast calls for Bill to turn further to the NW tomorow around the subtropical ridge over the Atlantic.  That northwesterly motion should continue for a couple of days before further turning steers the storm even more northerly at the end of the week.  All the models show this behavior for Bill.  Some are a little more aggressive with the NW to N turning by the end of the 5-day forecast period.  The rate of turning will likely only make a difference with whether Bill eventually hits eastern Canada or become extra-tropical and eventually makes his way to Europe.

The official intensity forecast calls for Bill to become a Category 3 storm by tomorrow night.  Bill is riding over 27.5C waters, which will only get warmer the further west he travels.  There are no regions of damaging shear forecasted to affect the storm within the next few days, so the environment is ripe for Bill to strengthen.  I think there is a decent chance that Bill might be a Category 3 between 12p and 6P local time (Bill’s) tomorrow.

The tropical wave that exited Africa after Bill has no chance of development.  There is a wave behind the first that is just now starting to move over the Atlantic.  This wave isn’t as vigorous as the one that spawned Bill, but more impressive than the wave that generated Ana.  It’s riding close to 10N, which would give it extra time as it crosses the Atlantic to develop.  Relativey low SSTs, and cooler waters stirred to the surface by Bill will act as inhibitors of tropical development.  In fact, we might have to wait for a couple of waves to come off before conditions are really favorable again.

Atlantic Tropical Weather Update 8/17/09 #2

Hurricane Bill has strengthened since this morning’s update at the NHC.  Hurricane Bill now has sustained winds of 90mph, which makes him a strong Category 1 storm.  Wind speeds need to be sustained at 96mph to be designated a Category 2 storm.  That will happen within the next 6 hours – Bills’ minimum pressure has decreased from 987mb to 977mb.  Intensification will continue throughout today and tomorrow.

Atlantic Tropical Weather Update 8/17/09 #1

As of today, Tropical Storm Claudette made landfall southeast of Fort Walton Beach, FL.  She has weakened to a Tropical Depression xince.  The threat from this storm remains torrential rainfalls and flooding, as has been the case during her brief lifetime so far.  Her center’s location is 31.3N, 87.2W; she has maximum sustained winds of 35mph.

Tropical Storm Ana couldn’t fight off the dry Saharan air that accompanied her off of Africa last week.  She weakened to a Tropical Depression yesterday before crossing over the Lesser Antilles near Guadeloupe.  Now in the northeastern Caribbean, T.D. Ana‘s vitals are as follows:

Center located at 16.7N, 64.8W; moving WNW @ 28mph; maximum sustained winds of 35mph.

T.D. Ana’s track forecast has shifted since yesterday.  She is expected to hit Hispanola more directly tomorrow than forecasted before, which will all but kill this storm with its extremely high terrain.  She will re-emerge over the Atlantic north of Cuba Wednesday, then she could possibly move between Cuba and Florida on her way to the Gulf of Mexico as a remnant low.  It is unlikely at this time that she would restrengthen to a Tropical Depression or Tropical Storm.  Time will tell, however, as Ana has beat the odds once already.

Bill is the bright point of the 2009 Season from a meteorological point-of-view.  As expected, Tropical Storm Bill strengthened to Hurricane Bill overnight.  His vitals this morning are:

Center located at 13.8N, 44.0W; moving WNW @ 22mph; maximum sustained winds of 75mph; minimum pressure of 987mb.

Hurricane Bill has the classic look of a healthy storm, with strong outflow to all quadrants of the storm and banded thunderstorms.  He hasn’t developed an eye-wall yet, but that should happen later today.

Hurricane Bill’s official track forecast continues to keep it out to sea during the remainder of his life, in line with all the model output.  Fortunately, that track keeps him to the north/northeast of the Antilles.  At most, they appear likely to receive only storm surge and the outer bands of the storm.  That track is typical of Cape Verde storms like Bill.  The only question at this time is whether a weakness in the subtropical ridge forms, which might allow for a deviation in the forecasted storm motion.  We’ll have to wait a couple of days to see whether that occurs or not.

Hurricane Bill should continue to steadily strengthen over the next couple of days, becoming a Category 2 hurricane by tomorrow morning and a major hurricane (Category 3+) late Tuesday night or Wednesday morning.  Thereafter, Bill should modulate in strength through days 4&5.