BMS Tropical Update 8/28/2015 12PM CDT

Tropical Storm Erika continues to defy forecasts made earlier in the week. At this point in time Erika was supposed to be much further north of the island of Hispaniola and in a much better overall environment for intensification. However, Erika is currently 90 miles southeast of Santo Domingo, DominicaRepublic, in an environment that is not at all conductive to tropical cyclone development.

 

Erika_TrackError2015

TS Erika NHC forecast made Tuesday afternoon showing the track error as Erika continues to defy forecasts

This further westward movement calls for drastic changes to the probabilities forecast options provided in my last update as we play another round of model roulette. In the last update I highlighted the overall uncertainties in tropical cyclone forecasting, and Erika has definitely met expectations with regard to those uncertainties.

Tropical Storm Erika continues to battle an incredibly unfavorable environment. The wind shear, which acts to tear apart tropical cyclones, is already quite strong – about 20 mph from the west – and it is forecast to increase to nearly 30 mph today. That amount of shear is hard for a well-developed storm to fend off, and Erika isn’t even well developed , which increases the overall probability of dissipation.

ShearAndTendency

Erika is in a area of 20 kts shear and is moving into an areas where shear could be as high as 30 kts. Tropical storms / hurricanes don’t like areas of high shear.

If Erika manages to make it over the mountains of Hispaniola intact and fight of this high shear area, she could quickly intensify again in the extremely warm waters off the coast of Florida. In fact history would suggest a tropical storm tracking up the west coast of Florida could be quite destructive such as the 1935 Labor Day hurricane.

Here is my updated break down of Erika’s forecast options at the moment:

  • Stalled hurricane in the Bahamas (0% chance) – Unlike the last update, this is now the least likely option for Erika, given its westward track.
  • Hurricane landfall in south Florida (30% chance) – A category 1 hurricane near south Florida on Monday morning with the storm stalling over the state of Florida during the middle of next week.  This would caused 6-8” or rain to fall over much of the state.
  • Tropical storm landfall in south Florida, but a hurricane on the Florida panhandle (35% chance) – Maintain a west-northwest heading, gradually intensifying and heading for south Florida as a tropical storm. Then tracking into the western Gulf of Mexico and becoming a hurricane along the west coast of Florida and into the Florida panhandle.
  • Death in the Caribbean (35% chance) – Failure to reach the mainland U.S.; and the storm stays further south and tracks over Hispaniola, Cuba, and maybe even northern Jamaica.

Once again there are forecast uncertainties and one can’t rule out Erika playing more forecasting tricks over the weekend as this weak disorganized system tries to stay alive. Hispaniola is historically a tropical cyclone blender.  If the NHC forecast is correct with a tropical storm landfall or close encounter to Florida much of the state may well be affected by the storm’s rainfall.  The last tropical cyclone to make landfall on south Florida was tropical storm Bonnie on July 23, 2010. Before that, the previous one was tropical storm Ernesto on August 30, 2006.  So indeed named storm activity has been very sparse since the wild 2004 and 2005 seasons.

Remember that  tropical storms are still quite capable of causing flash floods and power outages, as well as coastal erosion and flooding, and the winds can throw around unsecured loose objects. Tropical cyclones can also cause insured loss, case in point tropical storm Bill impacting Texas earlier this June.

Looking ahead there are no other tropical systems that should develop in the Atlantic Ocean next week.

BMS Tropical Update 8/26/2015 12PM CDT

Since my last update on Monday at noon, Erika has formed into a tropical storm and is tracking toward the Bahamas. Erika is currently 285 miles east of the island of Antigua in the western Caribbean. Tropical storm watches and warnings are out for many of the northern Caribbean islands. However, the headliner is that for the first time in three years, Florida is under the National Hurricane Center’s (NHC) forecast track cone of uncertainty. With a Florida landfall probability of 30%, there is a very real possibility that the 10-year Florida landfalling hurricane drought could end.

However, I must remind all readers about the overall uncertainties with forecasting hurricanes more than five days in advance. The uncertainty exists for a few reasons. First, the NHC track forecast errors over the past five years are 180 miles at day 4 and 240 miles at day 5, which are represented in the NHC cone of uncertainty. Secondly, intensity errors can also be large. Finally, this season is an El Niño year, which seem to be notorious for major hurricanes that start late in their careers. Betsy in 1965, Alicia in 1972, and Andrew in 1992 all took time to develop, but each El Niño year resulted in a major hurricane.

To demonstrate how a forecast can change look at what happen 10 years ago today as Katrina was moving off the Coast of Florida. In the loop below you will notice how the NHC forecast cone of uncertainty on Auguest 26th 11 am 2005 change in just a 12 hour period. This pivotal shift in Katrina’s forecast track occurred on Aug 26, 2005 moving from a FL panhandle landfall to LA/MS.


It should also be noted drastic forecast improvements of 40% have been made to hurricane track since 2005 which is show in the following plot of Katrina than and what it would be now.

KatrinaBefore_After

 

The forecast models for Erika are currently all over the place. Many meteorologist and various media outlets may continue to play model roulette, but the fact remains that Erika’s forecasted track and intensity is uncertain. Further, as I highlighted on Monday, we have to consider Erika’s overall weather pattern in light of the fact that the peak of the hurricane season is just 15 days away. Forecasters need to consider El Nino characteristics which include tropical waves and storms that may struggle in the main development region of the Atlantic Ocean. But as these storm move closer to the U.S. coastline, they will be more likely to develop and strengthen. These factors can’t be seen in any one forecast model run.

With Erika still 1,500 miles away from Miami, tropical storm Erika is still disorganized. However, Erika has plenty of time get organized. At this time, several factors support a gradual strengthening of Erika:

  1. The vertical wind shear, which can tear storms apart, is not very strong. However, until Friday, wind shear will continue to limit development. So if Erika can survive wind shear this week, as discussed in Monday’s write up, the change in the weather systems will cause shear to decrease as Erika tracks closer to the U.S.
  2. Less environmental dry air is getting wrapped into the circulation, which can disrupt thunderstorm development.
  3. The ocean temperatures below the storm are becoming increasingly warm.
  4. The ocean heat content is increasing along the storm’s forecast track.
TCHP_8262015

Lots of hurricane SST heat potential in the Bahamas, SST’s are 29-29.5 degrees Celsius. Could mean rapid intensification

Here’s how I’d break down Erika’s forecast options at the moment:

  • Death in the Caribbean (5% chance)  – Failure to reach the mainland U.S.; storm stays further south and tracks over Puerto Rico, Hispaniola. But it’s looking less likely at this point.
  • Weak tropical storm landfall in the Florida panhandle (15% chance) – Maintain a west-northwest heading, avoiding the Greater Antilles, and gradually intensifying and heading for south Florida as a tropical storm (then tracking into the Gulf of Mexico and becoming a hurricane along the west coast of Florida).
  • Hurricane landfall in south Florida (30% chance) – A Category 1 or 2 hurricane near south Florida on Monday (as suggested by the historically accurate European model (ECMWF), along with the high-resolution U.S. Hurricane Weather Research and Forecasting (HWRF) model). The HWRF model has been especially insistent on this.
  • Stalled hurricane (50%) chance. – Maybe at this time, the most likely scenario would be a hurricane tracking over the Bahamas near Florida where it will get trapped by weak atmospheric steering currents for a few days.

 

ErikaOptions

850mb wind and surface pressures from four dynamical models, all valid on Sunday evening. (tropicaltidbits.com)

 

It is important to note “impacts” of hurricane can occur many hundreds miles away from the cone of uncertainty: rain, storm surge, and strong winds could certainly occur outside of this cone.    In the next post I can start to focus in on the insured impacts.

Fun Fact:
In addition to frequent flights into Erika by hurricane hunters, a NASA Global Hawk drone was scheduled to embark on a 24-hour mission in and around the storm on Wednesday.

 

 

BMS Tropical Update 8/24/2015 12PM CDT

This is a quick tropical-storm update for the group as activity in the Atlantic Ocean heats up this week.

You might have noticed named storm Danny is no longer a threat and has been discontinued by the National Hurricane Center (NHC). Instead, it is now an open tropical wave as it approaches the southern shores of Hispaniola. However, there is a very slight chance that this open tropical wave could become better organized once again as it approaches the southern Gulf of Mexico this weekend, but this is a long shot at this point in time.

The new concern is a tropical wave that emerged off the West Coast of Africa last week. This tropic wave is currently has a 90% chance of development according the NHC and should be named storm Erika by tomorrow. The low pressure system is located about 1,250 miles east of the southern Lesser Antilles.

Why should soon to be named Erika be more of a concern than Danny?

First, this tropical wave is at a higher latitude. Danny started out at a latitude of 10.6 degrees north while this new tropical wave is at a latitude of 14.6 degrees north, which is a better location for intensification. Further, climatology indicates that this latitude is more likely to create a U.S. threating storm.

Secondly, Danny also was surrounded by dry, dusty air which limited its development in size and intensity. This new tropical wave will not have to fight as much of this dry, dusty air.

DannyDust

Dust and dry air as Danny was forming last week.

Dust824

Dust and dry air as TD5 is trying to organize.

Notice how much less dust and dry air is around this tropical wave versus the dust and dry air around Danny last week.

Thirdly, an upper-level trough has brought a taste of fall to much of the East Coast. As the trough slowly lifts out of the East Coast this week, upper-level winds will be much more conductive to less shear in the Atlantic Ocean.

 

0_5dayHeights

ECMWF 5 day anomaly chart which suggests cooler temperatures lower air pressure (blue area) along the East Coast of the U.S.

Day5

ECMWF next weeks (Day 5 – 10) anomaly chart which suggests warmer temperatures and higher air pressure (orange area) along the east coast of the U.S.

As you can see, next week’s forecasted weather pattern is much different than this week’s. Although there is some uncertainty in the track and intensity with any named storm forecast. Overall, next week’s weather should allow what will be Erika to track much further northwest ward toward the Bahamas as a hurricane. In fact, Erika could be a major hurricane by the time it reaches the Bahamas on August 30th given the warm sea surface temperatures near the islands. It is a bit early to determine how much of a U.S. landfalling threat Erika will be, but most storms near the Bahamas need to be watched, and this will be the case the first week of September.

HWRFERIKA_824

0z Aug 24 HWRF model Run Erika

The HWRF model, which did a great job with the intensification of Danny late last week, This model now provides a view of my general thinking as Erika tracks towards the Bahamas.
HWRF modeled 126 hour forecasted wind speeds of soon to be Erika.

Named Storm Fred could also develop behind Erika later this week, but let’s worry about Erika first.

Updates as needed or ask if you have questions.