31 August 2009

Disturbance closing in on Leeward Islands...

The easterly wave I mentioned on Friday has still not been upgraded to a Depression or Storm, but certainly looks like a weak Tropical Storm on satellite imagery.  It is now located about 600 miles east of the southern Leeward Islands and heading WNW at 12kts.  Nearly every computer model forecasts it to intensify to a hurricane by mid-late week.  SSTs in its path are 28-29C, and vertical wind shear is minimal (and expected to remain so for several days).  The next name on the list is Erika.

Danny weakened as it approached the coast Friday night into Saturday and NHC ceased writing advisories on it before it was even near the US or Canada.

Please visit my tropical Atlantic headquarters.

28 August 2009

Danny expected to recurve short of US coast...

The disturbance that I mentioned in my previous update on Tuesday has since been upgraded to TS Danny and has tracked northwest toward the southeast US coastline.  As of this morning, Danny was located about 350 miles south of Cape Hatteras NC and heading NW at 9kts.  The storm has consistently been poorly organized, with an exposed low-level center and the convective activity displaced to the east of the center.  Latest intensity is 35kts and 1008mb, and that is not expected to change much as it makes its way toward the coast then gets pushed out northeastward, scraping the US/Canada coast.

Danny is forecast to be near Cape Hatteras overnight tonight, then near Cape Cod on Saturday evening, over Nova Scotia on Sunday morning, and Newfoundland early Monday morning.  However, the effects will likely be minimal since it's not a strong storm and it'll be moving rather quickly.

Elsewhere, another easterly wave exited the African coast on Monday and has gradually gotten better organized.  It's located about 650 miles WSW of the Cape Verde islands and has a 1010mb Low embedded in it.  It is strongly favored by computer models to become the next hurricane by the end of the weekend as it heads WNW toward the Lesser Antilles.

And finally, an easterly wave is just now exiting Africa today and also shows signs of development.  The next two names on the list are Erika and Fred.

Please visit my tropical Atlantic headquarters.

25 August 2009

New disturbance being watched north of Leeward Islands...

An easterly wave that exited Africa on Aug 18 (the same one that I mentioned was near 35W last Friday) has very slowly gotten better organized and is now centered near 22N 64W... or about 400 miles north of the Virgin Islands.  It is being invigorated by an interaction with an upper-level Low to its west.

This wave is expected to continue to develop over the coming days and follow a path not too different from Bill.  That is, head WNW toward the US coast, then recurve offshore and turn to the NE, passing by Nova Scotia and Newfoundland.  However, this system may get closer to the US coast than Bill did, and even has the potential to clip the extremities such as NC, MA, and ME this weekend.

Since my previous update on Friday, Bill exited the scene after brushing by Nova Scotia and hitting eastern Newfoundland.

Please visit my tropical Atlantic headquarters.

21 August 2009

Bill heads NW between Bermuda and US...

Not much has changed since my last update on Wednesday.  The storm has weakened a bit to 95kts and 957mb, and has begun its more northerly track to the west of Bermuda and to the east of the US coast... it's currently about 700 miles southeast of the North Carolina coast.  Although it won't make a direct landfall on Bermuda or the US, it will (and has been) produce very large waves on Bermuda and all along the entire eastern seaboard of the US and Canada.

Here are measurements being recorded by a buoy in Bill's path (wind/pressure and significant wave height):

And from Bermuda (surface observations and radar loop):
http://www.weather.bm/observations.asp (if it asks for username/password: guest/guest)

In the longer term, Bill is expected to scrape by Nova Scotia on Sunday, then Newfoundland early Monday as a potent storm... transitioning from tropical to extratropical.

Elsewhere, a couple of easterly waves are producing healthy convection in the far eastern Atlantic... one near 30W and one near 18W.  The majority of forecast models do not develop either of these, but that could change with time.

Please visit my tropical Atlantic headquarters.

19 August 2009

Bill strengthens to a Category 4 hurricane...

Since yesterday's update, Bill went from 90kts to 115kts and from a central pressure of 963mb to 950mb.  Those figures are as of 15Z today.  As I type this update, a reconnaissance aircraft is heading into the core of the storm to determine the latest winds and pressure.  Hurricane Bill is located about 1000 miles SSE of Bermuda and heading WNW at 16kts.  This motion is expected to turn more NW then N in the coming days, avoiding the US coast, but perhaps threatening Bermuda, Nova Scotia, Newfoundland.  Environmental conditions are favorable for additional strengthening, and Bill is forecast to reach 125kts before encountering higher shear and cooler water in 5-6 days.

If the aircraft presently investigating the storm finds anything significantly different than the current intensity, I'll likely send out another brief update, otherwise, it'll be tomorrow.

Please visit my tropical Atlantic headquarters.

18 August 2009

Bill a Category 2 hurricane...

Three days ago, Bill was a Depression.  Now it's a 90kt hurricane on a strengthening trend.  An reconnaissance aircraft left St. Croix this morning to investigate the storm, and will be arriving in the eyewall within a couple hours of this writing.  At that point, the intensity could be adjusted (the transition from satellite-only intensity estimates to in-situ aircraft measurements can sometimes result in a false intensity change if you're looking just at the numbers).

At 15Z today, Bill was located at 15.9N 51.2W and tracking WNW at 14kts.  Intensity was 90kts and 963mb.  The track will follow a WNW trajectory for the next few days, gradually becoming more NW then N as it heads into a weakness in the subtropical ridge in 4-5 days.  While this scenario spares the US coast, it puts Bermuda in the target zone this weekend.  The storm is expected to intensify further, reaching CAT3 or 4 status in the next couple of days.

Please visit my tropical Atlantic headquarters.

17 August 2009

Ana, Bill, and Claudette made for a full weekend...

What was TD2 made a slight comeback over the weekend, and was upgraded to Ana.  However, it still struggles to get better organized, and has since been downgraded to TD Ana.  Presently located between Puerto Rico and Hispaniola, it is being further shredded by the mountainous terrain on those islands.  The forecast track brings it over Hispaniola and into south Florida in three days, but only as a Depression.  The primary threat associated with it will be flooding.

The potent easterly wave I had been mentioning all of last week was finally upgraded to TD3 on Saturday morning, then TS Bill on Saturday afternoon, then Hurricane Bill on Monday morning.  It continues to strengthen as it heads WNW at 14kts.  The latest intensity is 80kts and 977mb.  One significant change from the end of last week is the projected track of Bill.  It has moved northward quite a bit, which should result in it recurving prior to reaching the US coast.  However, it could potentially mean big trouble for Bermuda by this weekend.  Bill should be in the vicinity of Bermuda as a very strong hurricane by then.

And finally, Claudette formed just off the Gulf coast on Sunday morning.  I believe it originated from the same easterly wave I referenced way back on August 1 when it exited the African coast.  On the 4th it was near 35W, on the 10th it was near 60W, and on the 16th it was near 85W.  Fortunately, it did not intensify very much before heading inland over the western FL panhandle on Monday morning as a 45kt Tropical Storm.

Please visit my tropical Atlantic headquarters.

14 August 2009

TD2 dissipates, easterly wave getting organized...

TD2 succumbed to the shear and dry air and is now just a tiny low-level cloud swirl with intermittent bursts of convection.  It will be watched for regeneration though, but is not much of a concern in the near future.

On first glance, the easterly wave behind TD2's remnants looks very similar, but it is a much larger circulation, has its primary inflow from the south rather than the north, and the moderate vertical shear will be letting up within the next 12-18 hours.  Given these conditions, it is forecast to gradually intensify as it heads W-WNW.  At its current speed, it would be near the Lesser Antilles on Wednesday, quite possibly as a hurricane.
Although it's presently only 600 miles west of Africa, long-range models (8-10day) are already painting an ominous picture for the US coast by late next weekend.  It's too far out to say exactly where, but the timing at least serves as a heads-up for coastal residents.

Recall from my update three days ago that the last time the first named storm formed this late in the season was Aug 17, 1992: Andrew.

Please visit my tropical Atlantic headquarters.

13 August 2009

TD2 barely holding on...

Since yesterday, TD2 has seemingly ingested quite a bit of that stable dry air I mentioned, and is now nothing more than a low-level swirl of clouds.  The small circulation is also especially prone to even moderate vertical wind shear, which it's experiencing.  These conditions combine to give a small likelihood that TD2 will reach TS intensity in the foreseeable future.
As of 15Z today, the intensity was estimated at 25kts and 1008mb and it was located about 1400 miles east of the Leeward Islands.

On the other hand, the easterly wave on its heels still looks like something to keep a close eye on.  It's presently about 250 miles SSE of the Cape Verde islands and tracking W at 12kts.  It's still disorganized, but has a very definite circulation, persistent convection scattered around the center, low vertical shear, 28C SSTs, and is embedded in a large pocket of deep-layer moisture.
This disturbance is expected to gradually develop and head WNW toward the Caribbean over the next 5 days.

Please visit my tropical Atlantic headquarters.

12 August 2009

TD2 slowly organizing...

A combination of low-level stable air and moderate easterly wind shear is keeping TD2 below Tropical Storm intensity.  The latest intensity estimate is 30kts and 1006mb, and still heading W at 11kts.  The forecast track has changed very little since yesterday.  TD2 is still expected to reach TS status later today.

Elsewhere, the potent easterly wave I referenced yesterday has now exited the African coast and will be monitored for development.  Several computer models suggest this could become a storm to cause concern in the distant future.

I wanted to point out that my webpage at http://einstein.atmos.colostate.edu/~mcnoldy/tropics/atlantic/ is a little different... I reorganized the links.  So you might need to hunt around a bit at first to find your favorite resources, but hopefully the new system will work out better for people.

Please visit my tropical Atlantic headquarters.

11 August 2009

Second Tropical Depression of the season forms in far eastern Atlantic...

Two and a half months after TD1 formed off the northeast US coast, TD2 forms near the Cape Verde Islands off the west coast of Africa.  This is peculiar in two ways: it's rather late in the season to have the second Depression form, and it's rather early to have the "Cape Verde season" kick in.  The easterly wave that became TD2 was over Chad on August 4, and exited the African coast on August 8, so it has been a feature of interest for some time.  There's actually another potent easterly wave now located over Guinea, but that'll be a topic for a future discussion.

At 15Z today, TD2's intensity was estimated at 25kts and 1006mb.  It is located at 14.6N 29.6W and tracking W at 11kts.  It is embedded in an area of dry air (negative factor), it is over 27C water (neutral factor), and is in an area of minimal vertical shear (positive factor).  By this weekend, it may begin to feel a weakness in the subtropical ridge begin to move a bit more NW, potentially avoiding the Lesser Antilles.

It is forecast to become Tropical Storm Ana within a day, but maintain weak TS status for the near future.
The last time the second Depression formed this late in the season was 2000 (August 13, became TS Beryl).  The last time the first named storm formed this late in the season was 1992 (August 17, became Hurricane Andrew).

Please visit my tropical Atlantic headquarters.

04 August 2009

Easterly wave making its way across Atlantic...

On August 1, a potent African easterly wave exited the coast and is now centered near 35W.  There is evidence of a mid-level circulation in the satellite imagery, and a hint of a weak surface circulation based on microwave scatterometer and visible satellite data.  It has also maintain a small cold cloud shield over the center of the mid-level circulation.  This system, though poorly organized now, could become better organized in the coming days.  It would reach the Lesser Antilles this weekend if it holds together.

Elsewhere, the basin is quiet.  However, this is not atypical... climatologically, there is only one tropical storm by this date, and no hurricanes.  The first name on this year's list is Ana.

Please visit my tropical Atlantic headquarters.