30 September 2011

Ophelia now a major hurricane

Against all odds, the storm that was not even a Depression three days ago is now a 100kt major hurricane... the 3rd major hurricane of the season.  Since the 27th at 21Z when Ophelia regained Depression status, the maximum winds increased 75kts and the central pressure fell 48mb.  More impressively, we can narrow the time window down to the past 12 hours, when the winds increased by 25kts and the pressure fell 19mb.

This rapid intensification was not anticipated by dynamical models, statistical models, or human forecasters, and goes to show how little we still know about what makes these storms tick.  One run sticks out, which suggests it was more serendipitous than skillful... HWRF's 18Z run on Sep 27th was fairly accurate:

Ophelia is now forecast to maintain Category 3 intensity for another day or so, then gradually weaken and become extratropical by early next week as it gets whisked into the north central Atlantic by a strong mid-latitude trough.  Something to keep an eye on is Buoy 41049, which should get a near hit from Ophelia on Saturday afternoon: http://www.ndbc.noaa.gov/station_page.php?station=41049.  The winds are already on the rise there, the pressure is falling, and the significant wave height is up to 10 feet and increasing rapidly.

Philippe hasn't been so fortunate.  Still a 45kt tropical storm, it is battling relentless vertical shear, and will continue to do so for several more days.

In the plot below, you can see the track forecasts taking it generally westward over the next 5 days, and the shear forecast highlighting an unpleasant week for Philippe.  The official intensity forecast is in line with the statistical models on that plot (LGEM, DSHP, SPC3), and weakens the storm to a Depression by the end of the weekend.

Please visit my tropical Atlantic headquarters.

29 September 2011

Fourth hurricane of the season

At 21Z today, Ophelia was upgraded to a 65kt hurricane, the 4th of the season.  This is still a record low number of hurricanes for having 16 named storms though.  Looking back through the records, any season with 16+ named storms had at least 7 hurricanes.

The storm intensity guidance is from satellite estimates, since there aren't any aircraft in it, and it's not too close to any buoys.  The central pressure is down to 987mb, with a forecast for additional strengthening over the next couple of days.

Please visit my tropical Atlantic headquarters.

Ophelia nearly a hurricane

The easterly wave that exited the African coast on September 16 became TS Ophelia on Sep 21, then on the 25th was so weak that it wasn't even classified as a Depression.  A couple days later, it regained Depression status, then yesterday it regained TS status, and today, after this tremendous comeback, it is almost the season's 4th hurricane!  The images on this page allow you to easily track the appearance of this system over the past week: http://einstein.atmos.colostate.edu/~mcnoldy/tropics/hovmoller/epac_carib1/

At 15Z this morning, Ophelia is a 60kt TS with 991mb central pressure.  The microwave image below shows quite clearly that the storm has formed an eyewall, though the eye hasn't cleared out yet in infrared imagery.

The forecast is for some additional strengthening over the next couple of days as it heads north toward Bermuda.  Then as it comes under the influence of a mid-latitude trough, the shear will increase, and as it enters the north-central Atlantic, the SSTs will decrease.  Together, these effects will transform Ophelia into an extratropical cyclone within 4-5 days.

Moving on to Philippe... not much has changed.  The storm is still embedded in a strong vertical shear environment, so the deep convection associated with the Low is displaced completely to the northeast of the surface circulation.  At 15Z, the intensity estimate is 40kts and 1005mb... located about 1240 miles west of the Cape Verde islands.
The forecast is looking more interesting with time.  A large-scale ridge is expected to move back over the central Atlantic, which would steer eastern Atlantic systems more to the west (the current trough in place has been pulling everything north).  So despite the shear remaining fairly high during the period, the SSTs will at least be warm, and Philippe should be several degrees north of the Leeward Islands by the middle of next week.

Please visit my tropical Atlantic headquarters.

28 September 2011

Ophelia makes a comeback, and Philippe struggles

Since my last update on Monday, the remnants of Ophelia made a comeback.  The vertical shear decreased a bit more than expected, and the storm was surprisingly quick to take advantage of the improved environment.  It was upgraded to a Depression on Tuesday afternoon, and at 15Z this morning was upgraded again back to a Tropical Storm.  Though it's still in nearly 20kts of shear, convection has remained much closer to the center than it was a couple of days ago.  The latest intensity is 45kts and 1002mb.

You can view a radar loop of Ophelia from Guadeloupe at http://einstein.atmos.colostate.edu/~mcnoldy/tropics/ophelia11/Ophelia_27-28Sep11.gif
Although it's currently meandering very slowly, it is forecast to accelerate to the north within a day, and like Maria, reach hurricane intensity for the first time thanks to baroclinic enhancement as it interacts with a mid-latitude trough.  It should remain safely east of Bermuda when it passes by there on Saturday.

TS Philippe has a very similar appearance on satellite, but is a little weaker: a 35kt storm with 1006mb central pressure.  The forecast varies greatly depending on whether you're looking at a statistical models or dynamical models.  The official forecast agrees with the statistical models (LGEM, SHIPS, etc), by the way.

Please visit my tropical Atlantic headquarters.

26 September 2011

Ophelia dissipates and Philippe forms

Since my last update on Friday, Ophelia succumbed to the strong vertical shear and lost its tropical characteristics... namely, co-located persistent deep convection.  The final advisory was written on Sunday afternoon, and it's currently being tracked as a remnant low with a slight chance of regeneration... located northeast of the Leeward Islands.

Also since Friday, the disturbance I mentioned in the far eastern Atlantic was upgraded to TD17 shortly after my update was sent out, then upgraded again to TS Philippe on Saturday afternoon.  Philippe is the 16th named storm of the season... climatologically we would have just 8 named storms by this date.  Amazingly, 2011 is on par with the hyperactive 2005 season (in 2005 we were at the 17th named storm by this date).  As of this morning at 15Z, Philippe is a 50kt tropical storm located 600 miles west of the Cape Verde islands.

Philippe is also struggling with fairly strong vertical shear, as well as moderate SSTs (27C)... it should continue to maintain TS intensity as it recurves to the north in the coming days.  The 500mb chart below shows a deep trough in the central Atlantic that is responsible for recurving this storm so quickly.

Please visit my tropical Atlantic headquarters.

23 September 2011

Ophelia still struggling, new disturbance in far eastern Atlantic

Over the past couple of days since my last update, not much has changed with TS Ophelia... the storm reached 55kt intensity, but has been plagued by very strong vertical shear.  At 15Z today, it's down to a generous 35kts, with a forecast for additional weakening.  In the satellite image below, you can see the exposed surface circulation near 15N 53W with a convective blowup to the north, but the bulk of the convection displaced far to the east.  It's in about 20-25kts of southwesterly shear, and over the next 5 days, that is not expected to let up at all.

As you can see from the plot below, the models have backed off significantly on their intensity forecasts, and their high-shear environments all agree in the near term (GFS is quite a bit larger several days out, and that is the model that the DSHP and LGEM intensity models are based on).

Elsewhere, a fresh easterly wave exited the African coast yesterday and is presently south of the Cape Verde islands.  This wave was born over the Ethiopian Highlands 8 days ago and has a history over the past 3-4 days of being convectively active.  It appears likely that this system will be our next named storm: Philippe.

Please visit my tropical Atlantic headquarters.

21 September 2011

TS Ophelia forms

[This is the second and final update being sent to both the old and new mailing lists.  Check to make sure you are receiving this with tropatlan@googlegroups.com in the "To" field.  There are still quite a few people who have not migrated to the new list.  If you need any assistance or have questions, please ask.]

The easterly wave that exited the African coast on Sep 16 was upgraded to Tropical Storm Ophelia at 03Z today.  This is the 15th named storm of the season... climatologically by this date we would have just 7 named storms!

A fairly recent ASCAT overpass from 12Z shows a nice closed surface circulation with TS-force winds in the north half (ASCAT is a satellite-based microwave scatterometer which is able to retrieve surface wind speed and direction over water by detecting the surface roughness caused by winds disturbing the ocean's surface).

At 15Z this morning, Ophelia's intensity was estimated at 50kts with a minimum central pressure of 1005mb.  It's located about 1100 miles east of the Lesser Antilles and tracking W at 14kts.  It's being sheared, so the intensification has likely leveled off and it will continue to the W-WNW over the next several days as a TS.  The official forecast places it just north of Puerto Rico in 5 days as a TS, and the majority of model guidance supports that scenario.

Please visit my tropical Atlantic headquarters.

19 September 2011

New disturbance in eastern Atlantic

[This message is the first being sent to both the old and the new email lists.  I apologize for duplicate mailings, but I want to give everyone a chance to migrate and accept the invitation to the new Google Groups list.  If you have not yet accepted the invitation I sent on Friday (there is a link to click in that message... the subject was "Google Groups Invitation: Tropical Atlantic Update"), you will stop receiving these updates once I discontinue the old list.  The old distribution address was tropical@atmos.colostate.edu, and the new address is tropatlan@googlegroups.com.  Please check with me if you have any questions or problems!]

Over the past week or so, 3 easterly waves left the African coast.  But rather than making their way westward one after the other, they have begun to accumulate in a weak-steering region between 35-40W.  There's some evidence of this if you look at the time series of infrared images over the deep tropics: http://einstein.atmos.colostate.edu/~mcnoldy/tropics/hovmoller/atlantic/   In this view, the newest image is on top, and then you look back 12 hours every slice as you go down the page.  This allows you to track persistent features (such as African easterly waves) for many days simply by looking at their convective signature!  The visible satellite below shows the appearance of this disturbance as of this writing, with the surface center location marked by a red dot.  The estimated intensity is 25kts and 1008mb, and it's very close to becoming a Depression (TD16).  The next name on the list is Ophelia.

The plot below shows the past, present, and forecast intensity, track, shear, SST, and mid-level humidity.  The important thing to take away from it is that significant development of this is not expected in the near future, mostly because the vertical shear will be rather high.

Please visit my tropical Atlantic headquarters.

16 September 2011

Maria becomes season's third hurricane

After 9 days in the deep tropics since it was first classified as a Depression, Maria was upgraded to a hurricane at 21Z yesterday... making it the 3rd of the season (after Irene and Katia).  The extratropical transition is underway, and though it won't be classified as a hurricane much longer, it will remain a powerful extratropical cyclone with hurricane-force winds as it heads across the northern Atlantic toward Greenland and Iceland.  As of 15Z today, it is a 65kt hurricane with a 983mb central pressure... located just offshore of Newfoundland and racing NE at 45kts.

You can follow Maria on radar (until it zips out of view anyway) at http://www.weatheroffice.gc.ca/radar/index_e.html?id=WTP

Also, we've gotten lucky again with a buoy... Buoy 44251 is presently just 34 miles west of the center, and is reporting the following as of this writing (you can follow up later and see the full trace at http://www.ndbc.noaa.gov/station_page.php?station=44251):

Please visit my tropical Atlantic headquarters.

14 September 2011

Maria strengthens slightly

Over the past two days since my last update, Maria has barely maintained intensity in the 45-50kt range, due to the strong vertical shear.  Since Tuesday morning, the central pressure fell 5 mb... the only sign of vigor it has shown lately.  At 15Z today, the intensity is 50kts and 1001mb.  The low-level center (marked by the red dot on the image below) is still on the far fringe of the deep convection in the face of 15kt shear.

At about 06Z today, Maria passed just 20 miles west of Buoy 41046, and the buoy reported a surface pressure of 1004.5mb, along with sustained winds of 33kts, gusts to 43kts, and a significant wave height of 18 feet.  The wind and pressure trace also indicates a fairly weakly-organized core, with the pressure minimum coinciding with a tiny wind minimum and surrounded closely by wind maxima.  Quite a different look than the plot I showed from Katia's passage over Buoy 41048 six days ago!

Much like Katia, Maria is about to encounter a strong mid-latitude trough... and with that comes some baroclinic enhancement and an eventual extratropical transition.  So, in the coming couple of days, the storm could approach hurricane intensity even as the shear skyrockets and the SSTs plummet.  It will recurve between Bermuda and the US, with the closest approach to Bermuda occurring Thursday morning.

Please visit my tropical Atlantic headquarters.

12 September 2011

Nate makes landfall, Maria still a TS

Nate never made it to a hurricane, but that fits with the rest of the season.... only 2 of the 14 named storms have become hurricanes.  That's just 14% compared to the climatological 50-60%.  However, in terms of named storms, 2011 is just 1 behind the mega-season of 2005... by this date in 2005, we were on the 15th storm, and this year, we're on the 14th.  Tropical Storm Nate made landfall at about 1730Z on Sunday by Poza Rica.  The satellite image below is from the approximate time of landfall, and the full radar loop from Alvarado can be found here: http://einstein.atmos.colostate.edu/~mcnoldy/tropics/radar/index.html#nate11

Maria has been battling relentless vertical shear.  Now up to 30kts, the shear has displaced Maria's deep convection far to the east of the low-level circulation, as you can see clearly in the visible satellite image below (the surface center is near 21.7N 67.2W in this image). 
The intensity has been holding at 50kts for the past 30 hours, and the track has also been steady at WNW at around 8kts.  It is forecast to begin recurving to the north shortly, well before reaching the US, then pass just west of Bermuda on Wednesday night, then zip off into the north-central Atlantic.  It's still a possibility that Maria will reach hurricane status in 48-60 hours when it briefly could be exposed to less shear, and when it begins to experience baroclinic enhancement.

Elsewhere, a large easterly wave has just exited the African coast today, and has had a history of being very active since it formed over the Ethiopian Highlands on Sep 4.  It is not organized at all yet, but the surface pressure in coastal African stations fell to about 1011mb as it passed over, and is the next feature to keep an eye on over the coming week.

Please visit my tropical Atlantic headquarters.

09 September 2011

Katia, Maria, and Nate still making waves

Katia remains a strong Category 1 hurricane with 75kt winds as it recurves into the north central Atlantic.  It's over 26C water, in about 20kts of vertical shear, and is about to begin its extratropical transition (ET).  This will be a major storm for the UK early next week.

 The baroclinic enhancement that commonly occurs with ET can keep the intensity high even amidst what we typically think of as hostile conditions.  In the next 24h, the SST will plummet to 18C and the shear will increase to about 45kts, but the storm could still pack hurricane-force winds.  ET involves losing the circular symmetric structure and becoming more frontal in nature (which implies the cyclone tilts with height rather than being vertically stacked), while at the same time transitioning from a warm-core system to a cold-core system (which implies the strongest winds move outward and upward).  Tropical cyclones have their strongest winds at the surface and close to the center, while extratropical cyclones have their strongest winds aloft and quite removed from the center.

Maria has regained a lot of deep convection, and the intensity as of 15Z today is 40kts, with a forecast for VERY slow intensification over the next 5 days as it heads WNW toward the Bahamas.  Tropical Storm warnings cover the Leeward Islands and Puerto Rico (http://www.nhc.noaa.gov/storm_graphics/AT14/refresh/AL1411W5+gif/145220W_sm.gif). The vast majority of forecast models now indicate that Maria will follow a track similar to Katia, so as of now, it appears that the US east coast could be spared another rainmaker.

Nate is organizing and wrapping up, but part of what it's wrapping up is the very dry air from Mexico and the northwestern Gulf.  The entrainment of dry air into the system has limited its intensification, but it's still a 55kt tropical storm.  It is forecast to reach hurricane status by tomorrow morning as it crawls slowly westward toward the northern Veracruz coastline in Mexico.  There are hurricane and tropical storm watches/warnings around the Bay of Campeche's perimeter: http://www.nhc.noaa.gov/storm_graphics/AT15/refresh/AL1511W5+gif/143800W_sm.gif

Finally, it's worth noting that we are in the peak of the season now... Sept 10 is climatologically when we have the most activity in the basin: http://www.nhc.noaa.gov/climo/images/peakofseason.gif

Please visit my tropical Atlantic headquarters.

08 September 2011

Katia turns north, Maria struggles, and Nate strengthens

Hurricane Katia strengthened slightly to 80kts as of 15Z today, and did indeed pass over Buoy 41048 as expected -- the center of the eye was actually 34 miles west of the buoy at closest approach at 09Z.  It has also completed its turn to the north, and over the next few days will turn northeast and out into the north-central Atlantic graveyard.  However, it's only a graveyard for tropical cyclones... it will still be an extremely potent and dangerous extratropical cyclone as it heads for the UK early next week. 

Peak observations from the [un]lucky buoy include a 976mb pressure, 40-foot significant wave height, 68kt sustained winds, and 93kt wind gusts.  The SST dropped from its pre-storm value of 28.4C to a low of 25.1C!

Maria is still a 40kt tropical storm, but looks quite anemic this morning... a sign that shear and dry air are nudging their way into the vortex.

The plot below is the initial condition from HWRF's 06Z run... it's an along-shear cross-section of wind speed and relative humidity.  You can clearly see the asymmetry in the wind field (shaded), as well as the low RH values (contours) being forced into the system by the strong shear.  The official forecast brings Maria over the central Bahamas in 5 days as a strong tropical storm.  Given this track, the southeast and east coast of the US should be very alert... this is nearly a copy of Irene's track.

Tropical Storm Nate is at 45kts, and still virtually stationary.  It's forecast to slowly intensify to a hurricane on Saturday as it begins to crawl to the northwest toward the US/Mexico border next week.  You can view full-resolution visible images of Nate at http://rammb.cira.colostate.edu/ramsdis/online/loop_640.asp?product=tropical_ge_1km_center_relative_vis_floater

Please visit my tropical Atlantic headquarters.

07 September 2011

Katia, Maria, and Nate keeping the basin active

Hurricane Katia has not changed too much since my update this morning, but I wanted to highlight once again the buoy that it is going  to pass over.  It's a special occasion when a hurricane eye manages to pass directly over a tiny stationary buoy in the middle of the ocean.  And today, Buoy 41048 is that lucky one.  As of this writing, the buoy is 110 nautical miles NW of Katia's eye, and Katia is moving NW at 9kts (and a knot is a nautical mile per hour)... so that's about 12 hours until closest approach.  Already though, huge waves over 30' tall are rocking the buoy ("significant wave height" is defined as the average of the highest 1/3 of the waves), and wind gusts up to 54kts have been measured.  You can view current data and additional plots at http://www.ndbc.noaa.gov/station_page.php?station=41048

Maria is still a tropical storm, but I hunted through some historical tracks that matched Maria in terms of location, month, and intensity.  One very noteworthy result stuck out: Hurricane Hugo.  The track plot below shows Hugo's track, and the gray circle is a 100-mile circle around Maria's current location.  Hugo was located where Maria is now on September 13, 1989.  This of course doesn't mean that Maria will be a Hugo, but it's certainly worth paying close  attention to history.

Last but not least, the disturbance in the Bay of Campeche was upgraded to Tropical Storm Nate, the 14th named storm of the season, based on aircraft reconnaissance.  The intensity is 40kts and 1004mb, and it's basically stationary.  In such weak steering flow, a track forecast is extremely difficult to make, for both models and humans.  Models are all over the place with it, and justifiably so... but the official NHC forecast keeps it stationary for another 2 days, then ever so slowly tracks it northwest toward Mexico.  All of this time over the warm Gulf of Mexico should allow for some intensification, probably becoming the season's 3rd hurricane by the weekend.

Please visit my tropical Atlantic headquarters.

Katia weakens, Maria forms

Katia continues to lose its organization in the face of increasing vertical shear.  At 15Z today, the intensity is down to 75kts, and the forecast is for a very gradual weakening and loss of tropical characteristics. It is going to pass over a buoy located near 32N 70W later today... you can view observations (wave height, wind, pressure, etc) at http://www.ndbc.noaa.gov/station_page.php?station=41048  The infrared image below shows Katia, then Bermuda is the yellow speck near 32N 65W, and the buoy I mentioned is shown by the red dot.

Shortly after I sent out yesterday's update, the easterly wave that was near 35W was upgraded to TD14.  Then 18 hours later (15Z today), it was upgraded to Tropical Storm Maria, the 13th named storm of the season.  Maria's estimated intensity is 45kts with a 1003mb central pressure.  It's located at 13N 42W (about 1300 miles east of the Lesser Antilles) and cruising westward at 20kts.  The environment that it's in is only marginal for intensification... the SST is a healthy 28C, but the vertical shear is 12kts and increasing.  So, it will probably just slowly strengthen over the next several days, while tracking WNW toward the northern Leeward Islands.  This is a storm to keep a very close eye on if you're on the US coast; though at this point it's too early to say if it's heading for the Gulf coast or the east coast.

The trailing end of a front extending from the northeast US through Florida and into the Gulf of Mexico has been showing signs of organization.  The front ends in the Bay of Campeche, and the pressures are dropping in the area... with this disturbance at approximately 1007mb.  The 06Z surface analysis shown below illustrates the position of the front, and the terminal Low in the Bay of Campeche.  Also note the Low in western VA/NC associated with the remnants of TS Lee.

The steering flow in this area is very weak, so it's not going anywhere in a hurry.  It's also surrounded by dry air, so even if it does make to a TD or TS, it shouldn't get much stronger.  If named, the next name on the list is Nate.

Please visit my tropical Atlantic headquarters.

06 September 2011

Katia becomes season's 2nd major hurricane

The intensification trend I mentioned in Sunday's update did indeed continue, and on Monday at 21Z, Katia was upgraded to a Category 3 storm with 100kt sustained winds... then just six hours later, was upgraded again to a Category 4 storm with 115kt winds.   In the 18-hour period from 09Z on Monday through 03Z today, the pressure fell 26mb and the winds increased by 30kts.
As of 15Z today, the intensity is down a little to 105kts with a central pressure of 954mb.
The tiny yellow speck you see on that image near 32N 65W is Bermuda... and they now have a tropical storm watch in effect.  Models are now in excellent agreement on the track, and they indicate a recurvature by about 72W, safely off the US east coast, and safely west of Bermuda (though Bermuda could certainly feel some outer effects like tropical storm force winds and very large ocean swells).
The shear is also expected to increase again, and the mid-level relative humidity is quite low, so it appears that Katia will be on a steady weakening trend now until it ends up in the TC graveyard of the north central Atlantic.

The easterly wave that exited the African coast on Sep 2 (AL95) is now near 35W, or almost 1800 miles east of the Lesser Antilles.  It continues to show signs of organization, and will likely be upgraded to TD14 or even TS Maria within the next 24-48 hours.  The environment it's moving into isn't the best, so if it does develop, it should be slow to intensify for the next several days.  It is very far from land, but it will be something to keep a close eye on simply because of its location and potential track (the southeast US is about 11 days away).

Please visit my tropical Atlantic headquarters.

04 September 2011

Katia rapidly intensifies, Lee makes landfall

Not much changed since my last update on Friday... Katia has been hovering on the 60-65kt mark, which also means switching between TS and hurricane each time (fairly big name shift for a very minor change in wind speed).  The vertical shear has been much slower to let up than forecast (except for the GFDL model, which did see this extended period of high shear, but it was an outlier), and as a result, Katia did not intensify as forecast... but also didn't weaken much either.  However, conditions have improved over the past few hours, and the storm was quick to respond in a big way.  The intensisty as of 15Z today has skyrocketed up to 85kts with a central pressure of 966mb, and a open, clear eye is forming... it was a 60kt TS with a pressure of 992mb six hours ago!  The center is about 375 miles northeast of the northern Leeward Islands.  The forecast is still for additional intensification, and for a continued northwest track; it's looking quite likely now that Katia will recurve prior to reaching the US east coast, AND stay to the west of Bermuda.

Shortly after my update on Friday, TD13 was upgraded to TS Lee based on aircraft recon.  Since then, it did not intensify much, but as expected, remained a large amorphous rainmaker, crawling along at 2-5kts.  It made landfall about 50 miles west of Morgan City with 40kt sustained winds.  But more importantly, the rain keeps falling. 
There has already been up to a foot of rain across the southern coast, from LA to AL, over the last 3 days.  More will come today and tomorrow. Lee should still be over southern LA for at least another day, then begin accelerating to the northeast ahead of a mid-latitude trough... tracking over MS, AL, and TN over the next 3-4 days.  The graphic below shows the estimated rainfall totals over the past 4 days in the region:

Please visit my tropical Atlantic headquarters.

02 September 2011

Katia hanging on, TD13 forms in Gulf

Katia actually went against model guidance again and weakened a bit to a strong tropical storm yesterday afternoon, but has since reintensified to a minimal hurricane (65kts, 991mb).  The vertical shear was quite a bit stronger than forecast, and it definitely took a toll on the storm.  However, with shear dropping from 20kts to 10kts over the next couple of days, Katia should be able to resume the previous strengthening trend.
The official forecast calls for gradual intensification to 100kts (Cat 3) over the next 5 days as it heads WNW... with a 5-day (Wednesday) position located about 500 miles north of Puerto Rico.  The long-term future is still too uncertain as to whether it will recurve before reaching the US east coast or not, but extended-range models generally indicate a safe recurvature.  Certainly something to keep a very close eye on anywhere along the east coast though.

The disturbance that I first mentioned on Tuesday has been upgraded to TD13, and is not far from becoming Tropical Storm Lee.  This disturbance was way back by the Lesser Antilles on Aug 25, so it's been "on the radar" for a week now.  It is organizing very quickly now that the vertical shear is relaxing -- from 25kts to 5kts over the next 24 hours.  The intensity is 30kts, it's centered just 190 miles southwest of New Orleans, it's nearly stationary, and the outer rainbands are already onshore.
Tropical Storm warnings are up for the entire LA and MS coast... the latest forecast track, watches, and warnings can always be found at http://www.nhc.noaa.gov/storm_graphics/AT13/refresh/AL1311W5+gif/145613W_sm.gif

The 5-day accumulated precipitation forecast from HPC is still very ominous for the southeast, with 1-2 feet of rain possible over southern LA and MS.  You can watch the regional radar loop showing the extent of the rainfall at http://radar.weather.gov/Conus/southmissvly_loop.php 

This flooding rain will be combined with perhaps multiple days of tropical storm force winds, and I wouldn't be surprised at all if some evacuations were ordered for New Orleans, Biloxi, Mobile, Pensacola, and other urban flood-prone cities in the area (as well as offshore oil rigs).  If you or someone you know is down there, keep a close eye and ear to the local tv and radio stations this weekend.

Finally, the circulation that was north of Bermuda yesterday has not moved much at all, but is actually even more sheared than it was... making any development unlikely.  What convection there is in association with this system is displaced far to the northeast, and while the SSTs are fairly high now (28C), they will plummet to 22C within a day as it moves to the northeast.

Please visit my tropical Atlantic headquarters.