28 June 2012

Easterly wave struggling

With Debby well offshore and extratropical, it's time to focus on the easterly wave that I mentioned in yesterday's update.  It left Africa nearly a week ago, and is now near 43W, or about 1300 miles east of the Windward Islands.  The visible satellite image shows a small area of convection located near the diffuse wave axis:

It's in about 10kts of shear, and at the leading edge of a large envelope of high TPW (total precipitable moisture) as shown below.
And again, you can use http://andrew.rsmas.miami.edu/bmcnoldy/tropics/hovmoller/atlantic/ to track its journey... a new sliver of an infrared image of the deep tropical Atlantic is added every 12 hours, allowing you to go back several days and find persistent, trackable features, such as easterly waves!
This may be my last post about this wave unless it gets better organized... as it stands now, it may not be a trackable entity for much longer, and the global models are not too optimistic about it.

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27 June 2012

Debby makes landfall and crosses Florida

At about 21Z on Tuesday (5pm EDT), Debby made landfall near Steinhatchee FL as a minimal tropical storm.  Of course, for such a broad disorganized system, landfall is a bit anti-climatic.  Here is the visible satellite image near the time of landfall, showing the strongest storms northeast of the center and smaller but still potent thunderstorms associated with rainbands extending much further south...

Upon making landfall, Debby was downgraded to a Tropical Depression, and as of this post (1230Z), is exiting Florida as a very sloppy elongated Depression, and merging with a frontal system.

The updated rain total map shows the 20"+ areas extending further east across northern Florida, and isolated areas south of Tallahassee did receive an amazing (and destructive) 30" of rain in just a few days. 

Something else to keep an eye on, but far away from land... there's an easterly wave that exited the African coast back on June 22 and is now centered near 35W.  You can monitor is trek across the Atlantic at http://andrew.rsmas.miami.edu/bmcnoldy/tropics/hovmoller/atlantic/, and I'll discuss it further in the coming days if it shows signs of organization.

Finally, an update about my website... if anyone has it bookmarked (or any of its subpages), be aware that they've all moved to http://andrew.rsmas.miami.edu/bmcnoldy/.  Products on the old site will not be updated effective today.

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26 June 2012

Stubborn Debby barely moving

Tropical Storm Debby remains disorganized with very little deep convection near the center, but as history has taught us, even a weak tropical storm is capable of being destructive.

By far, the biggest issue associated with Debby is the rainfall, as expected.  Parts of the Florida panhandle have received nearly 25" of rain in the past few days (much of that came in in the past day), but the bulk of Florida has gotten 6" or more.  To add to that, an additional 3-6" is expected over northeastern FL in the coming few days.  The two plots below show the observed precipitation over the past 5 days, while the one below shows the forecast precipitation over the next 5 days.

As of 12Z today (8am EDT), Tropical Storm Debby has peak sustained winds of 40kts and a 991mb central pressure.  It's centered about 85 miles west of Cedar Key, FL and drifting east at 3kts.  It is expected to come ashore on Wednesday morning between Apalachicola and Tampa as a tropical storm. 

Again, the biggest threat will be additional heavy rain, and the exact timing and location of landfall makes little difference.  As far a storm surge goes, some areas in western FL could see up to 6' above normal tidal levels, particularly in Waccasassa Bay, Withlacoochee Bay, Crystal Bay, and Homosassa Bay.  You can find additional details and maps of storm surge products at http://www.nhc.noaa.gov/refresh/graphics_at4+shtml/090410.shtml?gm_esurge#contents

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25 June 2012

Heavy rain, tornadoes, and storm surge continue with TS Debby

Tropical Storm Debby is showing once again that a storm does not need to rank high on the Saffir-Simpson scale to be destructive.  Not even a hurricane, Debby is capable of producing overwhelming amounts of rain, moderate storm surge, and the threat of tornadoes.  On Sunday, as of this writing, there were nearly 20 preliminary tornado reports in Florida, and ~10 severe wind reports. The storm also turned deadly on Sunday when a Debby-spawned tornado destroyed a woman's house in central Florida.  Tornadoes will continue to be a possibility today through much of Florida, both in the peninsula and panhandle.  The two graphics below show the observed precipitation over the past three days, and then the tornado and severe wind reports from Sunday.

As far as rain goes, that's the primary concern as you might guess from the first graphic.  Debby has already dumped over a foot of rain on the west-central FL peninsula, and more can be expected in the same areas as the storm sits stationary offshore.  Local amounts in Hernando and Pasco Counties are in the 18-20" range already over the past 3-4 days.  The current regional radar loop is at http://radar.weather.gov/Conus/southeast_loop.php

As of 12Z today, Debby is a sloppy and disorganized 45kt storm, centered about 90 miles SSW of Apalachicola and 190 miles WNW of Tampa.  The rain coverage around the storm has decreased, but there are still strong rainbands wrapping around the center.  Tropical Storm warnings cover the entire coast of the FL panhandle, and will for the next several days... perhaps into the weekend.  The FL peninsula as well as southern AL and GA can expect periods of heavy rain and potentially severe weather all week.

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24 June 2012

Debby stalls, and forecasts change

TS Debby has been a challenge for forecasters long before it was named Debby.  It was an amorphous blob of convection in the western Caribbean a week ago, and most models agreed on SOMETHING happening, but not on when, where, how strong it would get, or where it would go.  Now that it's a full-blown named tropical storm, the uncertainty hasn't improved much. 

 Since this morning's post, the official forecast reflects Debby lack of motion, and now just has the storm drifting north over the next 5 days into the Florida panhandle with only modest intensification.  Tropical storm warnings extend from Alabama across to the Florida peninsula, as seen below.

This of course presents a giant problem with flooding.  A stationary or nearly stationary tropical system near land is a recipe for devastating flooding, and we are already seeing the beginning of that.  In the FL panhandle, storm surge as high as 6 feet is possible, along with rainfall totals of up to 2 FEET.  As with any tropical cyclone on/near land, rainbands can also contain tornadic supercells.

Again, the southeast US composite radar loop can be found at http://radar.weather.gov/Conus/southeast_loop.php

This will be a significant storm for Florida, and should not be treated as a non-event because it isn't a hurricane.

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Debby forms in northern Gulf, threatens the coast

On Saturday at 21Z (5pm EDT), the disturbance in the Gulf was upgraded to Tropical Storm Debby based primarily on aircraft recon into the system.  On average, we only see the 4th named storm on August 23, and to have the 4th named storm form on June 23 shatters the previous record set by Dennis on July 5, 2005.  This is truly a remarkable season so far!  As of 12Z on Sunday, Debby is located about 200 miles south of Pensacola FL and drifting north at 2kts, with a slowwww turn to the west expected later today.  The maximum sustained winds are 50kts and the minimum surface pressure is 994mb.  Debby is forecast to continue intensifying, and perhaps reach hurricane status by mid-week.

There are tropical storm warnings in place along a large stretch of the northern Gulf coast, as shown here.  There is larger-than-normal uncertainty in the track forecast due to the very weak steering currents and wildly divergent model guidance, but the latest official forecast shows a westward drift for the next couple of days, then speeding up a little but still heading generally west toward TX or western LA.  Keep in mind that the size of the cone of uncertainty is fixed for a season, and does not reflect storm-specific uncertainties.

The biggest threat from Debby right now is the large amount of rain.  The forecast rainfall over the next 5 days is shown here, with the largest amount offshore, but substantial amounts over land.  Several oil rigs in the Gulf have already begun evacuations and are shutting down, and some coastal counties/parishes have declared a state of emergency.

Being so close to the coast does have one advantage... constant monitoring by land-based radars.  The latest composite shows the extent of the rain, and you can always view the most recent loop at http://radar.weather.gov/Conus/southeast_loop.php

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22 June 2012

Chris nearly gone, Gulf disturbance still organizing

In the past 24 hours, Chris went from a hurricane to a low-level swirl with minimal convection and is surrounded by stable air and stratocumulus.  Now located approximately 400 miles ESE of Newfoundland, it is in the process of completing its loop that the forecast called for.  Its time as a tropical entity is very limited now, as it's over 15C water.  This will likely be my last post about Chris.

However, the Gulf disturbance, AL96, is still something worth keeping an eye on.  [As an aside, since I've gotten some questions about this, before a system reaches Tropical Depression status, it is typically designated as an "Invest", or area of interest that is being closely monitored and regional computer models are run on specifically.  These Invests are given the identifier of 9x, and they just run sequentially from 90-99 then start back over at 90 again.  The prefix is for the basin: AL is Atlantic, EP is East Pacific.  So, in a full season, there could be 5 AL93s and 4 EP93s.  Only once upgraded to a Depression does the system earn a unique identifier, such as AL04.]

The lowest surface pressure in the disturbance is ~1005mb now, and it's centered over the north-central Yucatan peninsula and barely moving.  While model guidance agrees on only minimal intensification, the agreement on the track forecast isn't as close.  As you can below, there is general agreement on a slow northward drift over the next 2-3 days, then after that, there's a bifurcation due to uncertainty in the strength of the ridge over the southern US.  So stay tuned!

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21 June 2012

Chris upgraded to hurricane, southern Gulf still brewing

An exceptionally rare and unforecast June hurricane is certainly not what anyone expected to be looking at today, but Chris took every opportunity to intensify.  At 15Z, the 65kt, 987mb hurricane was located near 41N 43W, or about 750 miles west of the Azores (don't get to reference those islands very often!).

Track guidance suggests that Chris will complete a little loop, then continue the northeast journey, passing north of the Azores but probably bringing some hefty weather to them in the coming days.

Elsewhere, the broad area of disturbed weather that was centered in the western Caribbean has oozed its way northwest as expected and is now roughly centered in the southeast Gulf of Mexico to the northern Yucatan peninsula.  It continues to show signs of organization, including a building mid-level circulation, a building anticyclone aloft, and persistent deep convection near the center.

An ASCAT overpass at 0327Z today (about 11 hours ago from this post) showed very tight curvature in the surface winds right off the tip of the Yucatan, but not quite a closed circulation.

Several models have become more aggressive with developing this system, and for the most part, agree with a slow crawl toward the north and a slow intensification.  This is still something worth keeping a close eye on for anyone along the northern Gulf coast (at this point, that includes Texas to Florida, perhaps with a little more weight toward the northeast Gulf coast).  If named, the next name on the list is Debby.  And climatologically, we only reach the "D" storm on August 23.  This would also be the first storm of the season to exist below 30N.  Of course, these are all contingent on it becoming more than a big cluster of thunderstorms!

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20 June 2012

Chris forms, Caribbean disturbance lingering

Shortly after my update yesterday, the area of interest that I mentioned southeast of Nova Scotia was upgraded to Tropical Storm Chris, the 3rd named storm of the season.  Climatologically, we don't see the 3rd named storm until August 13, so this is most definitely an active start to the season!
As of 09Z today (5am EDT), the intensity was 40kts and 1005mb, and it was located about 600 miles south of Newfoundland... no threat to land.

Elsewhere, the area of disturbed weather over Cuba and southern Florida continues to fester and spread copious rain over a large region. 
You can view a short radar loop from a mosaic of radars in Cuba at http://www.met.inf.cu/asp/genesis.asp?TB0=PLANTILLAS&TB1=RADAR&TB2=../Radar/NacComp200Km.gif

Whether or not this blob can organize into a TC is not a big factor in how much rain it will produce... huge rainfall totals will be observed over Cuba and southern Florida, and the the graphic below from HPC shows the forecast rainfall amounts over the next 5 days (not counting what has already fallen):

The lowest surface pressures associated with this system are around 1009mb now, and computer models are not very bullish when it comes to developing it.  Over the next several days, it should linger, with a slow drift to the northwest.  By the weekend, perhaps models will get a grip on what its next move will be.  But since it will be in the Gulf, coastal residents in the Gulf should keep an eye on it... just in case!

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19 June 2012

Two areas of interest in western Atlantic

There are a couple of areas of potential development: one is south of Nova Scotia and no threat to land, and the other is still a nebulous area of disturbed weather over Cuba and southern Florida.

First, the northern system.  This has been in the picture for several days now, but has gradually gotten better organized.  It has a chance of becoming a subtropical storm in the near future, but by Thursday, it will be too far into the north-central Atlantic TC graveyard.  It's presently about 400 miles southeast of Nova Scotia and forecast to head northeast.  It's presently over 23C water, and in 20kts of vertical shear, so while there is a possibility of this being classified as a named subtropical system, those chances are dwindling with time.

The southern system is an amorphous blob associated with a surface trough and a 1009mb Low over the western Caribbean. 

 The whole area is embedded in a wave of high TPW (total precipitable water), which is often a necessary condition for TC formation, and if nothing else, a key ingredient in heavy rainfall potential.  The loop below shows the westward movement of that higher TPW:

While this system is very disorganized now, it will still bring heavy rain to Cuba and southern Florida (perhaps up to 6"), and most likely drift NW toward Mexico or Texas over the next several days.  You can keep an eye on the rainfall over southern FL via Key West's radar: http://radar.weather.gov/radar.php?rid=BYX&product=N0Z&overlay=11101111&loop=yes

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