Atlantic Hurricane Season 2015

maquiladora

The Atlantic Hurricane Season doesn't officially start until June 1st but we might have a sub-tropical or tropical system in the next few days so might as well start the thread now.

For what it's worth, all the pre-season forecasts are going for a below-to-well below average season due to a number of climatic factors which could inhibit cyclone development.

Invest 90L is what is currently getting a bit of early attention.

1. Disorganized showers and thunderstorms extending over portions of
Florida, the Bahamas, and adjacent waters are associated with an
upper-level trough and a weak surface low located over the
northwestern Bahamas. The aircraft reconnaissance mission scheduled
for this afternoon has been cancelled. However, conditions are
expected to become gradually more favorable for development over the
next day or so while the system moves slowly northward. A
subtropical or tropical cyclone could form by Thursday or Friday,
and interests along the southeast coast of the United States should
monitor the progress of this system through the weekend. The next
Special Tropical Weather Outlook will be issued on this system by 8
PM EDT today. For additional information, see High Seas Forecasts
issued by the National Weather Service.

* Formation chance through 48 hours...medium...60 percent
* Formation chance through 5 days...medium...60 percent

maquiladora

1. Data from an Air Force Reserve Hurricane Hunter aircraft indicate
that the nearly stationary area of low pressure located about 210
miles south-southeast of the South Carolina-North Carolina border
is now producing 40-45 mph winds mainly to the north and west of the
center. Environmental conditions are favorable for some additional
development, and any increase in the organization of the associated
thunderstorm activity would result in the formation of a subtropical
cyclone. The low is expected to drift to the north or north-
northwest over the next couple of days, and interests along the
southeastern coast of the United States should continue to monitor
the progress of this system. Regardless of development, heavy rain
is expected over portions of the coastal southeastern United States
for the next few days. For additional information, see products
from your local National Weather Service forecast office and High
Seas Forecasts issued by the National Weather Service. The next
Special Tropical Weather Outlook on this system is scheduled for 8
PM EDT.

* Formation chance through 48 hours...high...80 percent
* Formation chance through 5 days...high...80 percent

.

maquiladora

The first named storm of the season, Subtropical Storm Ana is born.

hatrickpatrick

I don't really set too much store by long range hurricane season forecasts anymore. They've been unmitigated disasters for the last couple of years.

maquiladora

Not a major storm, just an early, interesting one. Could strengthen by about 10mph before landfall at most.

maquiladora

Ana has transitioned from subtropical to tropical and intensified to 60 mph. She will be approaching colder waters before making landfall tomorrow so may not have time to get stronger than that.

maquiladora

Invest 91L. Models currently not showing it to get any stronger than a weak TS but intensity is always hard to forecast.

maquiladora

Invest 91L is now Tropical Storm Bill and will make landfall in Texas later today.

Rikand

Atlantic hurricane season has always been my favourite from a weather watching perspective. Thanks for all the updates maq

maquiladora

Tropical Depression FOUR is born. Could be an interesting one. Tough conditions for cyclone development in the Atlantic this season but this one is probably worth keeping an eye on.

000
WTNT44 KNHC 181448
TCDAT4

TROPICAL DEPRESSION FOUR DISCUSSION NUMBER 1
NWS NATIONAL HURRICANE CENTER MIAMI FL AL042015
1100 AM AST TUE AUG 18 2015

The low pressure system that has been moving westward across the
eastern tropical Atlantic the past few days has finally acquired
enough organized deep convection to be classified as a tropical
cyclone. A 1232 UTC ASCAT-B overpass indicated the system has a
well-defined circulation, and there was also a large field of 30-kt
and greater wind vectors in the eastern semicircle. Dvorak satellite
intensity estimates are a consensus T2.0/30 kt from TAFB and SAB, so
the initial intensity is set at 30 kt for this advisory. Upper-level
outflow is good to the south and fair to the north.

The initial motion estimate is 280/11 kt. The global and regional
models are in good agreement on the tropical cyclone moving
west-northwestward along the southern periphery of a deep-layer
subtropical ridge for the next 48-72 hours, accompanied by a
decrease in forward speed as the system approaches a weakness in
this ridge. After that time, the ridge is expected to build back in
as a trough to the north lifts out, forcing the cyclone to turn more
westward and accelerate through the remainder of the forecast
period. The official forecast track lies close to but a little
faster than the multi-model consensus TVCN due to the much slower
GFS model creating a slow bias in the consensus.

The overall atmospheric and oceanic environments surrounding the
cyclone appear conducive for slow but steady strengthening
throughout the forecast period. The only inhibiting factor will be
occasional brief intrusions of dry mid-level air associated with the
Saharan Air Layer that lies just to the north of the depression.
However, given the very low vertical wind shear of less than 5 kt,
the convective structure is expected to steadily increase in
organization, allowing the dry air intrusions to be mixed out. The
official intensity forecast closely follows the intensity consensus
model IVCN through 72 hours, and then leans closer to a blend of the
Decay-SHIPS and LGEM models at 96 and 120 hours.

FORECAST POSITIONS AND MAX WINDS

INIT 18/1500Z 10.6N 36.5W 30 KT 35 MPH
12H 19/0000Z 11.0N 37.9W 35 KT 40 MPH
24H 19/1200Z 11.3N 39.5W 40 KT 45 MPH
36H 20/0000Z 11.6N 40.9W 50 KT 60 MPH
48H 20/1200Z 12.1N 41.9W 60 KT 70 MPH
72H 21/1200Z 13.2N 44.2W 70 KT 80 MPH
96H 22/1200Z 13.7N 47.8W 80 KT 90 MPH
120H 23/1200Z 14.0N 52.4W 85 KT 100 MPH

$$
Forecaster Stewart

maquiladora

Tropical Storm Danny is born.

maquiladora

Danny has become the first hurricane of the 2015 Atlantic season.

kevpants

I moved to the British Virgin Islands in March. This is my first experience with a Hurricane. I'm meant to fly to Miami on business on Monday. This is going to get interesting. Off to the supermarket for water and tinned food at lunch methinks.

hatrickpatrick

NHC now tracking three separate potential areas of interest in its five day outlook, one a subtropical disturbance with a 60% chance of development within five days, the other two being tropical waves off the African coast, so far with 30% and 20% development prospects, respectively.

So much for El Nino's hurricane season suppression...

maquiladora

The models are very keen on killing Danny. Official forecast now calls for weakening to kick in from tomorrow as Danny starts to encounter stronger wind shear.

maquiladora

Danny has reached Cat 3 status, the first major hurricane since 2011. No further strengthening is forecast as Danny will be encountering strong wind shear soon.

hatrickpatrick

maquiladora wrote: »

Danny has reached Cat 3 status, the first major hurricane since 2011. No further strengthening is forecast as Danny will be encountering strong wind shear soon.

My question is, what determines how soon a Cape Verde type tropical system recurves? It strikes me that they almost always veer northward around the time they reach the Lesser Antilles, and yet some of the most dangerous hurricanes to impact the United States do so because they remain on a primarily Westward track until they reach the gulf of Mexico, at which point they tend to rapidly intensify over warm waters before hitting a southern US state.

Thankfully most hurricanes over the last two or three years have recurved before they manage to reach the Gulf, meaning that the US has escaped landfalls, but what is it that determines how soon they turn northward?

maquiladora

hatrickpatrick wrote: »

My question is, what determines how soon a Cape Verde type tropical system recurves? It strikes me that they almost always veer northward around the time they reach the Lesser Antilles, and yet some of the most dangerous hurricanes to impact the United States do so because they remain on a primarily Westward track until they reach the gulf of Mexico, at which point they tend to rapidly intensify over warm waters before hitting a southern US state.

Thankfully most hurricanes over the last two or three years have recurved before they manage to reach the Gulf, meaning that the US has escaped landfalls, but what is it that determines how soon they turn northward?

If there is a persistent ridge across the Atlantic then the cyclone will continue westward towards landfall. A weakness in the ridge will allow the cyclone to recurve out to sea.

hatrickpatrick

maquiladora wrote: »

If there is a persistent ridge across the Atlantic then the cyclone will continue westward towards landfall. A weakness in the ridge will allow the cyclone to recurve out to sea.

Ah, this if I'm not mistaken then is one of the positive effects of El Nino for the US - the outflow from East Atlantic tropical cyclones means that upper level lows are more likely in and around the Western atlantic than highs, right?

Birdnuts

Is it just me or has the Atlantic hurricane season in recent years been very,very quiet??

hatrickpatrick

Jeff Masters has an interesting blog post up about a CCKW, a phenomenon I hadn't come across before, which he says is a very large scale upper air circulation currently drifting Eastwards across the Atlantic, and protecting Danny and the two emerging tropical wave which have been cited as possible future tropical systems, from El Nino's wind shear.

http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=3078

Birdnuts wrote: »

Is it just me or has the Atlantic hurricane season in recent years been very,very quiet??

Since 2012, we've had two quiet years. This year looked like it would be quiet, but it's ramped up so much in the last few days (well before the actual peak of hurricane season) that I wouldn't write it off just yet.

In 2013, the Sahara belched an absolutely humungous dust storm over the whole Atlantic just as the peak of the season was beginning. The dust choked tropical waves before they had time to develop, and because it was slow moving, it affected the Atlantic for all of August and most of September as well.

https://www.youtube.com/watch?v=F3Q8Sh2AjPo

Last year, 2014, we apparently flipped briefly to a negative AMO phase for the first time in years. So Atlantic Sea Surface Temperatures were a lot lower than normal. Also, although El Nino hadn't yet formed, the East Pacific was extremely active - I don't think I've ever noticed a category 5 hurricane in the East Pacific before, and this one happened right in the middle of peak Atlantic season - which created the same hostile conditions in the Atlantic, albeit on a much smaller scale, as El Nino has this year. This is actually the same reason there were no tropical cyclones in July of 2012 - July saw three extremely powerful hurricanes form in the East Pacific, a cat 2, a cat 3 and a cat 4.

It's essentially to do with the Earth's rotation. Any major atmospheric events on the West coast of the US have the capacity to get blown over the continent and affect what's going on in the Atlantic. So when you see an active East Pacific, hurricane-wise, it probably means the Atlantic will be inactive for a time.

maquiladora

Danny has weakened to Cat 2. Continual weakening is forecast but the islands will probably get a tropical storm warning today.

maquiladora

Danny boy has degenerated into a remnant low. But Erika will be forming hot on his feel tonight or tomorrow. She could well run into the same problems with high sheer that Danny faced however.

hatrickpatrick

Anyone know why that new tropical wave behind invest 98L has been downgraded by the NHC? They're now saying it's very unlikely to develop, where before it left Africa they were saying 40% chance within 5 days. What's changed since then? You'd think Danny and 98L would have made enough inroads into the dry air to minimise that as a problem...

maquiladora

Tropical Storm Erika is born. Currently forecast to stay at TS strength due to increasing wind shear after 48 hours. Most recent runs of main global models don't really develop it because of this. Interesting track though.

(Having said that, the very latest ECM blows it up to a sub-950 hurricane at 240 :P)

Iancar29

maquiladora wrote: »

Tropical Storm Erika is born. Currently forecast to stay at TS strength due to increasing wind shear after 48 hours. Most recent runs of main global models don't really develop it because of this. Interesting track though.

(Having said that, the very latest ECM blows it up to a sub-950 hurricane at 240 :P)

Yep , here it is!



One to watch for sure

maquiladora

Latest GFS doesn't make anything of it, total contrast to the ECM.

Looking at the hurricane models, at the moment the majority have it approaching southeast US as a hurricane. Could well recurve out to sea before any landfall but it's far too early to say.

Conditions could be tough for the next several days and Erika first has to survive that much before anything else happens.

maquiladora

GFS is still refusing to develop Erika, but looking at the other models including the latest ECM then it seems a hurricane into south Florida in around 5 days is a real possibility. Something we haven't seen for a while.

maquiladora

Erika is up to 50mph. Still has a couple of days of stronger shear and islands to dodge in order to survive, but if she does survive all that then conditions should become much more favorable: low shear and very warm waters ahead. The models have been shifting around since yesterday morning and a south Florida landfall doesn't look likely now unless it stays quite weak. Northeast Florida to the Carolinas now looking more likely, but a recurve out to sea without any landfall is also very possible.
I think it'll be at least another 24 hours before we have a good idea what will happen.

Hooter23

Tropical Storm Erika: At Least 12 Dead, Widespread Flooding Reported in Dominica; State of Emergency Declared in Florida

As Tropical Storm Erika inches closer to Hispaniola, Florida Gov. Rick Scott wasted no time urging residents to prepare, declaring a state of emergency for all counties Friday morning.

Erika has already turned deadly. At least 12 people have been killed on the small island of Dominica, NBC News reported Friday morning.

"Erika has really, really visited us with a vengeance," Claude Weeks, assistance police superintendent, told the Associated Press during a phone interview. Because many roads and bridges are impassable, crews are trying to reach isolated communities via the ocean, he added.

Among those confirmed dead were a blind elderly man and two children in southeastern Dominica, and another man was killed in the country's capital of Roseau, the report said.

http://www.weather.com/safety/hurricane/news/tropical-storm-erika-preparations-caribbean-florida-impacts

maquiladora

Fred is born.