Hurricane Isaac – 6 am – Wednesday, August 29

Isaac has spent the last 12 hours bumping along the Louisiana coast, moving very slow to the west northwest.  It is currently located about midway between Cocodrie and Leeville near the Lafourche/Terrebonne Parish line.  Enough land interaction has started weakening the system.  The eye is starting to fill and most sustained winds are around 50 mph.  There are numerous areas in southeast Louisiana where winds are still gusting to between 60 and 70 mph.

The latest HRRR suggests that Isaac won’t move much during the day and by 6 pm will be located somewhere just north or northwest of Morgan City.

After today, guidance is extremely spread with one camp taking the decaying storm west northwest into Texas before curving north into Oklahoma… and another camp taking the system toward Shreveport before turning north through western Arkansas.  It’s very important for people in the path of Isaac to pay attention to forecasts during the next few days.  While the wind threat will slowly subside during the next 24 hours, Isaac has the potential to be an incredible rain maker with major flooding and flash flooding expected.  The tornado machine also seems to be turned on now with numerous tornado warnings having been issued between Mobile and New Orleans. 

There will be a sharp gradient of extreme rainfall associated with Isaac.  10 to 15 inches of rain will be possible over portions of central and eastern Louisiana, while southwest Louisiana may only see around an inch.  The heaviest rain will occur near and to the east of the center.

Hurricane Isaac – 6 pm – Tuesday, August 28

Isaac was named a hurricane by the National Hurricane Center at 11:20 am this morning… probably about 3 hours later than the upgrade should have been.  It currently is located about 15 miles south southwest of the mouth of the Mississippi River and moving to the northwest at about 8 mph.

Max winds are now 80 mph and the central pressure has dropped to 970 mb. 

There have been no changes to the watches or warnings and the system seems to still be having problems with dry air entrainment.  Otherwise, given the low pressure, one would expect this hurricane to have winds near 100 mph.  There have been platforms in the area and other buoys that have been reporting gusts to well over 90 mph.

Track guidance continues to be widespread ranging from central Arkansas to central Oklahoma during the 72 hour range.  Isaac is a large hurricane with effects spreading outward several hundred miles from the center.  Recent tornado warnings have been in effect for portions of the western Florida Panhandle in association with meso-cyclones embedded in rainbands. 

Everyone from the western Florida Panhandle to Arkansas and Oklahoma… eastern Texas and Louisiana should maintain steady updates on the progress of Isaac.  Flooding rains and tornadoes will be possible for the next several days.

Still Tropical Storm Isaac – 10:45 am – Tuesday, August 28

We will start with the current situation.  The isolated occurrences of data that supported Isaac becoming a hurricane this morning were not sufficient given the overall situation for the National Hurricane Center to upgrade the system.  Overall, winds are considered to be near 70 mph with a system that continues to get disrupted by various things – mainly dry air that gets entrained into the system destroying attempts at a solid inner core.  Fair enough, while it looks like there may have been a spot or two of sustained hurricane force winds this morning, the overall impression is still that Isaac is just a very large, and very strong tropical storm.  With a slower forward speed than this morning, it appears the storm has about 12 to 18 hours of possible strengthening before landfall.  During that time, it is still likely that Isaac will reach minimal hurricane strength.

The track forecast has been shifted slightly to the west, and that seems reasonable given the last hour of trend on radar.  It also falls toward an unexpected move by morning guidance which starts taking the system farther west again.  In some cases, almost back in line with the thinking of yesterday where south central Louisiana will come under the gun. 

Watch and warning changes with the latest NHC advisory include: The hurricane warning has been replaced with a tropical storm warning from the Mississippi/Alabama border eastward to Destin, Florida.  Also… the tropical storm warning has been discontinued east of Destin.

All other previous watches and warnings remain in effect.

One curious thing about the morning guidance is that many solutions have shifted the track back into Oklahoma at the 96 hour mark.  It should be noted that a lot of these models have also picked up on the current westward move by Isaac during the last few hours.  Now we have a broad area from Texas and Oklahoma eastward through Missouri, Arkansas, and Louisiana where people should pay attention to the progress of Isaac.  Landfalling tropical systems will often weaken considerably with regard to wind, but are still capable of producing flooding rainfall and tornadoes.

Tropical Storm/Hurricane? Isaac – 8:30 am – Tuesday, August 28

Various data is likely being evaluated at the National Hurricane Center, but it appears that a couple hours of strengthening have taken Isaac to hurricane strength.  Some air recon data indicates surface winds near 81 mph.  In addition, a 53 ft tall platform about 90 miles to the northeast of the center has sustained winds at 68 mph.  The radar presentation has improved with a nearly completely closed and constricting eye wall.  The last reported central pressure was down to 976 mb.  This is in line with some category 2 hurricanes.  With Isaac, the wind has had a hard time catching up to the pressure.  However, given the appearance and observations, it looks like Isaac may have finally fought the odds and reached low end category 1.  Now we wait for the next update from the National Hurricane Center.

Tropical Storm Isaac – 5 am – Tuesday, August 28

It’s hard to believe this morning that we are not calling it Hurricane Isaac.  Centered about 125 miles south southeast of the mouth of the Mississippi River, Tropical Storm Isaac has sustained winds of 70 mph.  The central pressure has fallen to 977 mb.  While there have been westward wobbles, the motion is generally northwest at about 12 mph. 

There are a good number of possibilities as to why Isaac is not a hurricane yet.  It has had trouble maintaining a strong, well defined inner core.  This may be due to dry air entrainment, or possibly the fact that the storm is very large and hasn’t been able to constrict.  For whatever the reason, environmental conditions still favor some strengthening.  Outflow is good, sea surface temperatures are warm and the storm should become a hurricane during the next 12 hours.  Of course, I’ve said that numerous times over the last couple of days.

Isaac is a very large storm with effects that extend very far from the center.  For that reason, there are a number of watches and warnings:

A hurricane warning:
From east of Morgan City, Louisiana to the Alabama/Florida border… including Metropolitan New Orleans… Lake Pontchartrain… and Lake Maurepas.

A hurricane watch:
From Intracoastal City to Morgan City, Louisiana.

A tropical storm warning:
From the Alabama/Florida border to the Aucilla River… and from Morgan City to Cameron, Louisiana.

A tropical storm watch:
From east of High Island, Texas to just west of Cameron, Louisiana.

One strong outer rain band is making its way across Plaquemines Parish at this time, and there has been a significant increase in wind at buoy sites near the mouth of the Mississippi River during the last few hours.  Conditions in the warning area will be deteriorating during the next few hours and preparations to protect life and property should be completed.

Intensity and track guidance has pretty much all come in line over the last 24 hours.  Isaac should make landfall around 4 pm this afternoon near Pilottown, or somewhere in Plaquemines Parish with hurricane winds of around 90 mph.  It’s important not to focus on the spot of landfall as this is a very large storm with far reaching effects.  After landfall, the storm will start to weaken, but still be capable of producing flooding rainfall and tornadoes as it tracks toward Arkansas.

Tropical Storm Isaac – 4 pm – Monday, August 27

Several indications point toward Isaac being at hurricane strength this afternoon.  The pressure has steadily fallen and is now estimated to be lower than 982 mb. Surface winds are starting to respond and are estimated at over 70 mph.  The satellite appearance is one of a low end hurricane with good banding, outflow and a developing organized central core.

 

There is a chance that the Hurricane Center will still hold the intensity at tropical storm strength on the next advisory, but it is very close.

 

Isaac is about 320 miles south southeast of Mobile, Alabama and moving to the northwest at 12 mph.

 

So where do we go from here?  Well, it looks like the slow but steady intensification process has started as the storm continues to look better and better organized, and recon data confirms that.  Latest intensity guidance suggests that the system will reach winds of near 100 mph at landfall – which will be in about 36 hours.  This is also carried by the National Hurricane Center.

 

Track guidance remains problematic with the most likely area of landfall just to the west of the mouth of the Mississippi River.  There is a wide range in guidance with outliers extending from the Texas/Louisiana border to Mobile, Alabama.  This results in the following watches and warnings:

 

A hurricane warning is in effect from east of Morgan City, Louisiana to the Alabama/Florida border.  This warning includes Metropolitan New Orleans… Lake Pontchartrain… and Lake Maurepas.

 

A hurricane watch is in effect from Intracoastal City to Morgan City, Louisiana.

 

In the warning area… preparations to protect life and property should be rushed to completion.  People in the watch area should seriously consider preparations based on their local area.

 

On either side of the hurricane watch or warning… there are likely to be tropical storm conditions. Tornado producing rain bands are still affecting Florida, and there will be tornado producing rain bands well inland either side of where Isaac makes landfall.

 

Longer term guidance has slowed in its western movement.  The possibility of the system making it all the way into Oklahoma at about 96 hours is becoming more and more unlikely with a path through Arkansas more likely.  There will be a chance of flooding rains and tornadoes associated with the decaying system all the way up to I-40 during the next few days.

 

In addition to the previously mentioned threats… the National Hurricane Center offers:

 

Storm surge… the combination of a storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters.  The water could reach the following depths above ground if the peak surge occurs at the time of high tide…

 

  • Southeast Louisiana and Mississippi… 6 to 12 ft
  • Alabama… 6 to 9 ft
  • South-central Louisiana… 3 to 6 ft
  • Florida Panhandle… 3 to 6 ft
  • Florida west coast including Apalachee Bay 1 to 3 ft

 

The deepest water will occur along the immediate coast in areas of onshore flow.  Surge-related flooding depends on the relative timing of the surge and tidal cycle…and can vary greatly over short distances.  For information specific to your area…please see products issued by your local weather service office.  Near the coast… the surge will be accompanied by large and dangerous waves.

 

Rainfall…Isaac is expected to produce additional rain accumulations of 1 to 3 inches over the eastern Florida Peninsula…with isolated storm max totals of 15 to 20 inches possible.  Total rainfall amounts of 6 to 12 inches… with max amounts of 18 inches are possible in southeast Louisiana… southern Mississippi…southern Alabama and the extreme western Florida Panhandle.

Tropical Storm Isaac – 3 am – Monday, August 27

Early this morning, Isaac was located about 160 miles west northwest of the Key West radar site.  The storm is moving to the west northwest at 14 mph.  Radar and satellite imagery show a system that has improved its appearance during the last six hours and would suggest that Isaac is a hurricane.  It has a large area of very cold cloud tops with good outflow, and radar shows a nearly closed eyewall.  However, air recon continues to find no support to suggest that the storm has reached hurricane strength and winds are held at 65 mph with a minimum pressure of 990 mb.  Given the appearance and current strength, it would only take one good little drop in pressure for Isaac to suddenly become a hurricane.

Given the environmental conditions, Isaac is expected to slowly, but steadily gain strength until landfall with forecast sustained winds near 100 mph.  Most all intensity guidance supports this.  The track guidance is in overall agreement in moving the system in the direction of the mouth of the Mississippi River over the next 36 to 48 hours.  From there, it becomes more problematic.  There is one camp of guidance that wants to turn the system northward toward the Louisiana/Mississippi border, and another camp of guidance that wants to turn the system more westward moving it along the Louisiana coast.  The spread in guidance has resulted in quite a large area of watches and warnings in advance of Isaac.  A hurricane warning is in effect from east of Morgan City, Louisiana to Destin, Florida.  This includes Metropolitan New Orleans, Lake Pontchartrain, and Lake Maurepas.  In these areas, preparations to protect life and property should be rushed to completion.

A hurricane watch is in effect from east of Destin to Indian Pass, Florida.

Numerous bands of convection are trailing the system and spreading over the Florida Peninsula.  With these, tropical storm warnings are in effect from Jupiter Inlet southward on the east coast and from Tarpon Springs southwest on the west coast.  Also included: The Florida Keys, Dry Tortugas, Florida Bay, Lake Okeechobee, and from east of Destin, Florida to the Suwannee River. 

Several strong meso-cyclones have been noted in the rain bands over Florida and isolated tornadoes will remain a threat.  Also, tornadoes will become a threat near and to the right of where Isaac makes land fall, and with rain bands moving on shore as early as this evening from southeast Louisiana to northwest Florida. 

Isaac should make land fall late Tuesday evening or early Wednesday morning (keep in mind that dangerous weather conditions will reach land well in advance of the center).  For a couple of days afterward, there will be a threat for flooding rains and tornadoes well inland.  While that area of forecast is highly uncertain, the operational GFS / which has been fairly reliable / suggests a track toward southwest and central Louisiana and then northward near the Oklahoma/Arkansas border.  However, anyone from east Texas to Alabama should be mindful of the threats that come from tropical systems after land fall and check on updates daily. 

 

Tropical Storm Isaac – 12 pm – Sunday, August 26

For the first time in its life, Isaac is trying to resemble an honest to goodness tropical cyclone early this afternoon.  Three quadrants of the storm look pretty decent, the exception being the southwest quad where some dry air and weak shear is still showing up.  Still, convection has been working around a narrowing center which is located about 50 miles southeast of the Key West radar site.  Max winds are still around 60 mph and no significant pressure drop has been noted.  Strong squalls have been moving westward through the Keys and south Florida.  Winds gusting to 40 knots have recently been reported in Key West, and a buoy just southwest of Key West has reported sustained winds to 43 knots.  Some of the activity on radar suggests low level meso-cyclones and some waterspout/tornado potential.  A tornado watch is in effect for roughly the southern half of Florida.

Short term guidance is in general agreement of moving the cyclone to the west northwest and gradually increasing it in strength.  Isaac is still likely to become a hurricane before it exits the Florida Keys.  Longer term guidance remains in line with previous thinking that the storm will not be picked up by the eastward moving U.S. trough as easily as earlier thought, and in fact may miss the system all together.  The result would be a steady course toward the mouth of the Mississippi River.  This has forced hurricane watches to be wrapped around the northern gulf coast as far west as  Morgan City, Louisiana.  The watch now includes the New Orleans Metro area and Lake Pontchartrain.  A hurricane warning remains in effect for the Florida Keys including the Dry Tortugas and the west coast of Florida from Bonita Beach southward to Ocean Reef.  Also included is Florida Bay.

There have been no significant changes in intensity guidance with Isaac still expected to have near 100 mph winds at landfall.  It should be noted that intensity and location guidance is held in very low confidence past 48 hours from now.  All interests along the gulf coast from the Texas/Louisiana border to southeast Florida should pay attention to the progress of Isaac.

Tropical Storm Isaac – 1 am – Sunday, August 26

I am starting to believe that Isaac is going to be a complete pain in the butt for forecasters.  I’ll start with what it is now.  Located about 65 miles northeast of Camaguey, Cuba, the storm is moving to the northwest and at a fairly solid rate of 17 mph.  The direction has shifted westward just a bit over the last 12 hours.  *Make note of that…    Maximum winds are near 60 mph and the pressure has fallen once again to 997 mb.  There have been some blowups of convection over water around the storm which is hugging the Cuba coast, but otherwise, the system continues to look quite ragged. 

I believe that for no other reason than continuity sake the National Hurricane Center is holding watches and warnings pretty much as is.  They include the hurricane warning for the Florida Keys including the Dry Tortugas.  A hurricane warning for the west coast of Florida from Bonita Beach southward to Ocean Reef… and Florida Bay.  A hurricane watch is in effect for the Florida east coast from Golden Beach southward to Ocean Reef.  A tropical storm warning is in effect for the Florida east coast from Sebastian Inlet southward to Ocean Reef… Lake Okeechobee… and the Florida west coast from north of Bonita Beach to Tarpon Springs… including Tampa Bay.  A tropical storm watch is in effect for the Florida east coast north of Sebastian Inlet to Flagler Beach and the west coast and panhandle north of Tarpon Springs to Indian Pass. 

Isaac is close enough to hurricane strength that people in the hurricane warning area should continue to make preparations to protect life and property.  Conditions preventing safe preparations will be deteriorating over the next 12 hours as the outer bands of Isaac approach. 

As far as what to do with Isaac in the future.  Guidance has made a marked shift to the west and is tightly clustered through 36 hours taking the storm center well into the Gulf of Mexico.  While this forecast takes the storm center well to the southwest of Tampa Bay, outer bands will still likely affect a lot of southern and western Florida.  People should continue to heed all watches and warnings for their local area.  Of greater interest now becomes the longer term portion of the forecast.  The eastern moving U.S. trough which was supposed to have an impact on the subtropical ridge steering Isaac is showing signs of staying far enough north and quick enough moving to not pick up the storm.  Instead, numerous solutions of recent guidance suggest the storm will take a straight as an arrow approach through the Gulf of Mexico with an eventual landfall near the mouth of the Mississippi River.  This change in solution is so quick and so dramatic that caution is required before jumping all in with it.  In fact, the National Hurricane Center continues to have its current forecast of landfall well east of the guidance consensus – near the western end of the Florida Panhandle.  I do believe that people now living all the way around to the southern coast of Louisiana should start to keep up daily with the progress of Isaac. 

Shear is expected to weaken over Isaac during the next 72 hours and most models suggest that the storm will be a solid Cat 1 storm over the northern Gulf.  How Isaac fares moving away from Cuba and the next 24 hours of model data will be extremely important in determining the final strength and location of landfall.

Tropical Storm Isaac – 8 am – Saturday, August 25

Waking up this morning, we find several changes in the thought process associated with Tropical Storm Isaac than we had last night.  First of all, while some disorganization has occurred while passing over western Haiti, it did not have quite the disruption that was anticipated.  Also, by staying on an almost straight northwest course, the center of the cyclone may manage to just clip the eastern tip of Cuba.  The bottom line (which interestingly enough was suggested by model guidance several days ago) is that Isaac may have taken the path of least land area as it now sets its aim toward Florida and the Gulf of Mexico.

 

The center of Isaac this morning is moving through the Windward Passage… or about 95 miles east southeast of Guantanamo, Cuba.  The central pressure has managed to remain below 1000 mb (998 mb), and sustained winds are about 60 mph.

 

The tight cluster of guidance we enjoyed yesterday has become more spread this morning.  There still seems to be a western weight which would take the storm through the Florida Keys, however, more of southern and western Florida would become into play if a few of the solutions verify.  A fairly large 24 hour forecast spread has developed.  For now, the National Hurricane Center is holding on to the most clustered area of track forecast which takes the hurricane through the Florida Keys during the very early morning hours of Monday.  This track, combined with the less land path Isaac has taken has resulted in southern Florida residents waking up this morning to hurricane warnings.  A hurricane warning is now in effect for the Florida Keys including the Dry Tortugas… Florida Bay… and the west coast of Florida from Bonita Beach southward.  A hurricane watch remains in effect for Haiti and the Florida east coast from Golden Beach southward.  A tropical storm warning remains in effect for the Florida east coast from Jupiter Inlet southward and Lake Okeechobee.  People in the hurricane warning area should rush to complete preparations to protect life and property.

 

With most guidance suggesting that Isaac will keep a track over water, intensity guidance has changed significantly since last evening.  The center of guidance has the storm reaching high end Cat 1 or low end Cat 2 strength.  Outlier guidance suggests that Cat 3 may be possible.  Almost all guidance suggests that there will be a possible period of rapid intensification 48 to 72 hours from now.  Additional watches or warnings will likely be required farther north along the west coast of Florida later today.

 

People living from near the mouth of the Mississippi River eastward through the west coast of Florida should pay close attention to the progress of Isaac.

 

In addition, rainband embedded tornadoes will become more likely by late this evening over extreme southern Florida.  This threat will spread northward through the southern half of Florida on Sunday… and across most of the state on Monday.  Adjacent areas of Alabama and Georgia will also be at risk by late Monday into Tuesday.