N. ATL Hurricane Season 2013 Discussions

[unome]

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TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT FRI JUL 5 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

1. A WEAK SURFACE LOW IS PRODUCING WIDESPREAD CLOUDINESS AND SCATTERED
SHOWERS AND THUNDERSTORMS OVER MUCH OF THE SOUTHWESTERN GULF OF
MEXICO. THE LOW IS EXPECTED TO MOVE NORTHWARD AT 5 TO 10 MPH OVER
THE NEXT COUPLE OF DAYS...AND MOVE INLAND ALONG THE TEXAS COAST BY
SUNDAY. DEVELOPMENT OF THIS DISTURBANCE...IF ANY...SHOULD BE SLOW
TO OCCUR DUE TO PROXIMITY TO LAND AND ONLY MARGINALLY FAVORABLE
UPPER-LEVEL WINDS. THIS SYSTEM HAS A LOW CHANCE...20 PERCENT...OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS. REGARDLESS OF
DEVELOPMENT...THIS DISTURBANCE WILL PRODUCE PERIODS OF LOCALLY
HEAVY RAINFALL AND GUSTY WINDS ACROSS PORTIONS OF UPPER TEXAS AND
SOUTHWESTERN LOUISIANA BY LATE SATURDAY NIGHT AND CONTINUING INTO
SUNDAY.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER STEWART
NNNN

[Ptarmigan]

The surface low in the Bay of Campeche is now Invest 94L.

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AL, 94, 2013070506, , BEST, 0, 221N, 960W, 20, 1012, LO, 0, , 0, 0, 0, 0,
AL, 94, 2013070512, , BEST, 0, 225N, 960W, 20, 1011, LO, 0, , 0, 0, 0, 0,
AL, 94, 2013070518, , BEST, 0, 229N, 960W, 20, 1011, LO, 34, NEQ, 0, 0, 0, 0, 1013, 150, 70, 0, 0, L, 0, , 0, 0, INVEST, S,

[Scott747]

Can't get any farther out there in fantasyland...

But the 0z GFS is at least a conversation piece.

[srainhoutx]

The 12Z NCEP Ensemble TC Genesis Probabilities are suggesting a future Dorian may be brewing. We will see.

[unome]

best use of music in a tropical update video I've ever come across..

https://www.facebook.com/photo.php?v=10 ... =2&theater

refreshing sense of humor

[Ptarmigan]

This is from the Canadian. It develops a storm in 6 days from a upper level low in the Central Atlantic. Other models do not develop anything from that upper level low.

[rnmm]

97L in the Gulf of Mexico, who woulda thunk it?!?!? WOW!

[David Paul]

http://my.sfwmd.gov/sfwmd/common/images ... orm_97.gif

[rnmm]

97L has been deactivated, it seems as it was a test according to the NWS NOAA Facebook page....

[TexasBreeze]

^^

We've gotten at least one phone call from someone wondering why guidance models were run on "Invest AL97" today, even though we're not mentioning anything in our Tropical Weather Outlook. This invest was started purely for testing purposes in connection with the planned transition to the new NWS supercomputer next week. Once the testing has been completed, the invest AL97 will be deactivated.

We know that people tend to follow these invest systems more closely now than in the past, but this should serve as a reminder that invests can be opened for a variety of reasons, not all of them meteorological.

[srainhoutx]

For the past 4-5 days the operational GFS and the NCEP TC Genesis Probabilities have suggested a strong tropical wave exiting the African Coast has some potential to develop. That trend continues today with additional reliable guidance suggesting the first Cape Verde storm of the season may develop next week. We will see.

[srainhoutx]

The quiet tropical Atlantic is showing signs of awakening. While the reliable models have been mixed, a cold tongue of ocean water in the Gulf of Guinea is very evident and tends to lead to the start of the African wave train. Across Africa we can see the evidence with increasing convection and the ITCZ is becoming a bit more active as well across the MDR. Over the next week to 10 days, we will need to monitor areas from 40W toward the Caribbean as the Saharan Arid Layer (SAL) is replaced with increasing moisture and potential for tropical spin ups or TC Genesis and the Cape Verde season begins. Another area to monitor will be the SW-W Caribbean as conditions become a bit more condusive for development as the monsoonal trough becomes active. Satellite imagery is clearly suggesting the tropical switch is about to be turned on as we begin the climb to toward peak season which will continue until mid September.

[srainhoutx]

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT MON JUL 22 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

1. A TROPICAL WAVE HAS EMERGED OFF OF THE WEST COAST OF AFRICA ABOUT
500 MILES EAST-SOUTHEAST OF THE CAPE VERDE ISLANDS. ENVIRONMENTAL
CONDITIONS ARE EXPECTED TO BE MARGINALLY CONDUCIVE FOR SOME
DEVELOPMENT OF THIS DISTURBANCE OVER THE NEXT FEW DAYS AS IT MOVES
WESTWARD AT 10 TO 15 MPH. THIS SYSTEM HAS A LOW CHANCE...10
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER STEWART

[TexasBreeze]

Now the National Hurricane Center will extend the Tropical Weather Outlook to 5 days out. Graphics will remain 2 days though till further notice. Starts August 1st 7am. From NHC homepage top headlines.

[srainhoutx]

There are rather strong indications that conditions much more conducive for Tropical development will spread E across the EPAC into the NATL Basin during the next 10 days or so. The reliable Euro Ensembles are suggesting a more favorable MJO pulse and Kelvin Wave will progress E into our part of the world around the August 6th-9th time frame +/- a couple of days. I believe during the mid August to early September time frame has the potential for multiple storms to develop. We will see.

[srainhoutx]

There are rather strong indications that conditions much more conducive for Tropical development will spread E across the EPAC into the NATL Basin during the next 10 days or so. The reliable Euro Ensembles are suggesting a more favorable MJO pulse and Kelvin Wave will progress E into our part of the world around the August 6th-9th time frame +/- a couple of days. I believe during the mid August to early September time frame has the potential for multiple storms to develop. We will see.

Right on cue...

[srainhoutx]

Glimmer of hope, 12Z GFS develops a depression in SRain's beloved 'Carla Cradle' in about 12 days and at Day 16 it could be a tropical storm and menacing Northeast Mexico.

Yes, I know, fantasy range GFS, but it isn't like this thread will be cluttered with real acticity the next week or so. Although 91L (Zombie Dorian) has been re-activated as an invest.

Yep, And the NCEP Ensemble TC Genesis Probabilities have been 'sniffing' that area for some potential development the past couple of days.

[Katdaddy]

Today marks the 43rd annivessary of Hurricane Celia that blasted the Corpus Christi, Texas area with winds gusting to 175-180MOH. Hurricane Celia was one of the 3 major hurricanes I studied while growing up along the Upper TX Coast. Carla 1961 and Beulah 1967 were the other TX major hurricane landfalls. Each storm had their unique attribute. Celia was a very small TC with RI ongoing at landfall which brought high velocity winds similar to Hurricane Andrew 1992, Carla was very large TC that brought a widespread storm surge to TX and LA. Beulah brought widespread major flooding to most of S TX from San Antonio down to Lower Rio Grande Valley as well as 115 tornadoes which was the record at the time. I studied these storms wonder what it would be like to actually experience a major hurricane. We had a few hurricane threats in the 70s which never materialized as well as a few tropical storms. Alicia in August 1983 answered my question. I have much respect for the power of TCs. Its a matter of time until another major hurricane strikes the TX Coast. Hurricane IKE was only a CAT2. CAT 3,4, and 5 are designated as major hurricanes. Its been 30 years this month since Alicia visited the Upper TX Coast and its been 52 years since Carla visited the Middle TX Coast. This is why I tell everyone to be ready each hurricane season. Its just a matter of time until another major hurricane hit. It could be the is year.

[srainhoutx]

The Global operational and ensemble guidance are coming into agreement that the current SAL (Saharan Air Layer) outbreak across the Atlantic Basin will begin to loose its grip and pressures will begin to fall across the MDR (Main Development Region) in about 10 days or so. The NCEP Ensemble TC Genesis Probabilities remain very bullish for development in the SW Caribbean Sea as the monsoon trough begins to lift N and a favorable MJO pulse begins to arrive in our part of the world. Right on cue, it does appear as we climb toward peak season, conditions may well become conducive for tropical development.

[srainhoutx]

NOAA’s updated 2013 Atlantic Hurricane Season Outlook continues to call for an above-normal season, with the possibility that the season could be very active. The outlook indicates a 70% chance of an above-normal season, a 25% chance of a near-normal season, and only a 5% chance for a below-normal season. See NOAA definitions of above-, near-, and below-normal seasons, which have been slightly modified from previous years. The Atlantic hurricane region includes the North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico.

As predicted in May, atmospheric and oceanic anomalies across the tropical Atlantic Ocean and Caribbean Sea (called the Main Development Region, MDR) are now conducive to an above-normal Atlantic hurricane season. These conditions are expected to persist throughout the peak months (August-October) of the hurricane season in association with the tropical multi-decadal signal, which has contributed to the high activity era that began in 1995. This signal is linked to above-average sea surface temperatures in the MDR and to an enhanced west African monsoon, both of which are now in place.

The presence of two named storms in the deep tropical Atlantic during June-July reinforces the expectation for an above-normal season. Historically, years with early-season activity in this region have a high likelihood of being above-normal, with many also being very active (i.e., hyper-active).

A third factor for the season is the likely continuation of ENSO-neutral conditions. There is only a low probability (19%) that La Niña will develop and further enhance the activity, and an even lower probability (8%) that El Niño will develop and suppress the activity.

Based on the current and expected conditions, combined with model forecasts, we estimate a 70% probability for each of the following ranges of activity for the entire 2013 Atlantic hurricane season:

•13-19 Named Storms
•6-9 Hurricanes
•3-5 Major Hurricanes
•Accumulated Cyclone Energy (ACE) range of 120%-190% of the median.


The seasonal activity is expected to fall within these ranges in 70% of seasons with similar climate conditions and uncertainties to those expected this year. These ranges do not represent the total possible ranges of activity seen in past similar years.

The expected ranges are centered well above the official NHC 1981-2010 seasonal averages of 12 named storms, 6 hurricanes, and 3 major hurricanes.

Activity to Date:
Four tropical storms (Andrea, Barry, Chantal, and Dorian) have formed in the Atlantic basin to date, with Chantal and Dorian forming in the deep tropical Atlantic. Significant activity is expected for the remainder of the season, with an additional 9-15 named storms likely, of which 6-9 are expected to become hurricanes with 3-5 reaching major hurricane status.

Changes from the pre-season outlook issued May 23rd:
All of the predicted ranges of activity have been lowered and narrowed slightly from the May outlook. Three reasons for these changes to the ranges are: 1) No hurricanes or major hurricanes formed during June and July; 2) The probability of La Niña developing during August-October is now low; and 3) Many models now have more conservative predictions of hurricane activity.

Hurricane Landfalls:
While NOAA does not make an official seasonal hurricane landfall outlook, the historical likelihood for multiple U.S. hurricane strikes, and for multiple hurricane strikes in the region around the Caribbean Sea, increases sharply for very active (or hyperactive) seasons (ACE > 165% of median). However, regardless of the activity predicted in the seasonal outlook, it only takes one storm hitting an area to cause a disaster. Therefore, residents, businesses, and government agencies of coastal and near-coastal regions are urged to prepare every hurricane season regardless of this, or any other, seasonal outlook.

Predicting where and when hurricanes will strike is related to daily weather patterns, which are not reliably predictable weeks or months in advance. Therefore, it is currently not possible to accurately predict the number or intensity of landfalling hurricanes at these extended ranges, or whether a particular locality will be impacted by a hurricane this season.

DISCUSSION

1. Expected 2013 activity

Climate signals and evolving oceanic and atmospheric conditions, combined with dynamical and statistical model forecasts, continue to indicate a high likelihood (70% chance) for an above normal 2013 Atlantic hurricane season, with a reasonable possibility that the season could be very active (i.e., hyperactive). The outlook also indicates a 25% chance of a near-normal season, and only a 5% chance of a below-normal season. See NOAA definitions of above-, near-, and below-normal seasons, which have been slightly modified from previous years.

An important measure of the total seasonal activity is NOAA’s Accumulated Cyclone Energy (ACE) index, which accounts for the combined intensity and duration of tropical storms and hurricanes during the season. This outlook indicates a 70% chance that the 2013 seasonal ACE range will be 120%-190% of the median. According to NOAA’s hurricane season classifications, an ACE value above 120% of the 1981-2010 median reflects an above-normal season, and an ACE value above 165% of the median reflects a very active (or hyperactive) season.

The 2013 Atlantic hurricane season is predicted to produce (with 70% probability for each range) 13-19 named storms, of which 6-9 are expected to become hurricanes, and 3-5 are expected to become major hurricanes. These ranges are centered well above the 1981-2010 seasonal averages of 12 named storms, 6 hurricanes and 3 major hurricanes.

Although this updated outlook is consistent with the pre-season outlook issued in May, all of the updated predicted ranges of activity have been lowered and narrowed slightly. These changes reflect: 1) The lack of hurricanes during June and July; 2) The latest CPC/ IRI ENSO forecast and many climate models which predict that La Niña is less likely to develop and further enhance the season; and 3) Some models are more conservative in their predictions of Atlantic hurricane activity.

To date, four tropical storms (Andrea, Barry, Chantal, and Dorian) have formed in the Atlantic basin, with Chantal and Dorian forming in the deep tropical Atlantic. For the remainder of the season, an additional 9-15 named storms are expected, of which 6-9 are likely to become hurricanes with 3-5 reaching major hurricane status.

For the U.S. and the region around the Caribbean Sea, the historical probability of a hurricane landfall generally increases with increasing seasonal activity. During very active seasons, the historical probabilities increase markedly for multiple hurricane strikes in these regions. Nonetheless, predicting the location, number, timing, and strength of hurricane landfalls is ultimately related to the daily weather patterns, which are not reasonably predictable weeks or months in advance. As a result, it is currently not possible to reliably predict the number or intensity of landfalling hurricanes at these extended ranges, or whether a given locality will be impacted by a hurricane this season. Therefore, NOAA does not make an official seasonal hurricane landfall outlook.

2. Science behind the 2013 Outlook

The continued high confidence for an above-normal season is based on several factors. First, conducive atmospheric and oceanic conditions have developed across the MDR, as was predicted in May. Second, these conditions are expected to persist throughout the peak months (August-October) of the hurricane season in association with the tropical multi-decadal signal, which has contributed to the Atlantic high activity era that began in 1995. This multi-decadal signal is linked to above-average sea-surface temperatures in the Main Development Region (MDR, which spans the Caribbean Sea and tropical Atlantic Ocean between 9oN-21.5oN; Goldenberg et al. 2001), and to an enhanced west African monsoon system. Recent SST analyses and tropical circulation analyses show that both of these conditions are now in place. Third, early-season activity in the deep tropics (Tropical Storms Chantal and Dorian) is generally indicative of an above-normal season. Fourth, ENSO-neutral conditions are expected to persist through August-October.

The outlook also takes into account dynamical model predictions from the NOAA Climate Forecast System (CFS), the European Centre for Medium Range Weather Forecasting (ECMWF), the EUROpean Seasonal to Inter-annual Prediction (EUROSIP) ensemble, along with ENSO (El Niño/ Southern Oscillation) forecast models contained in the suite of Niño 3.4 SST forecasts compiled by the IRI (International Research Institute for Climate and Society).

a. Expected continuation of tropical multi-decadal signal


The main guiding factor behind this updated outlook is the expected continuation of the tropical multi-decadal signal (Goldenberg et al. 2001, Bell and Chelliah 2006), which has contributed to the current high-activity era in the Atlantic basin that began in 1995. This signal incorporates the warm phase of the Atlantic Multi-decadal Oscillation (AMO) and an enhanced west African monsoon system, both of which are in place again this summer. It is associated with inter-related atmospheric conditions that are conducive to increased Atlantic hurricane activity.

During 1995-2012, some key atmospheric aspects of the tropical multi-decadal signal have included weaker easterly trade winds and reduced vertical wind shear in the MDR. The weaker trade winds are already present. They are associated with a more northward location and more conducive structure of the African Easterly Jet (AEJ), including increased cyclonic shear along its equator-ward flank. This position and structure of the AEJ strengthens African Easterly waves moving westward from Africa, and directs them westward over progressively warmer ocean waters and weaker vertical wind shear. During August-October, these waves and their associated convective cloud systems are responsible for the vast majority of Atlantic hurricanes and major hurricanes.

During July, the weaker vertical wind shear was not yet well established across the MDR, and instead was variable in association with strong intra-seasonal variability partly linked to the Madden- Julian Oscillation (MJO). Therefore, although the climate signals point to an above-normal season, the shorter-term variability in the vertical wind shear lends uncertainty as to how strong the season will be. If the shear remains highly variable, then the activity could be near the lower end of the predicted ranges. If the shear weakens further, which would be consistent with the expected climate patterns, then the activity could be near the middle or higher end of the predicted ranges.

b. Expected above-average SSTs in the Main Development Region


The second factor guiding this outlook is the expected continuation of above-average SSTs across the MDR throughout August-October. This expectation is based on current observations, the ongoing warm phase of the AMO, and CFS T-382 model forecasts.

June-July sea surface temperatures measured over the entire MDR were 0.10oC above-average, and were also 0.09oC warmer than the remainder of the global tropics. While this relative warmth is somewhat less than in some recent years, it is consistent with the ongoing high-activity era for Atlantic hurricanes, and with the continued expectation for an above-normal Atlantic hurricane season.

c. ENSO-Neutral conditions


ENSO is another climate factor known to significantly impact Atlantic hurricane activity. The three phases of ENSO are El Niño, La Niña, and neutral. El Niño tends to suppress Atlantic hurricane activity, while La Niña tends to enhance it (Gray 1984). These typical impacts can be strongly modulated by conditions associated with a low- or high-activity hurricane era.

The combination of a high-activity era, above-average Atlantic SSTs, and ENSO-neutral conditions historically produces active or very active Atlantic hurricane seasons. ENSO-neutral conditions have been present throughout the summer. SSTs are currently slightly below average across the east-central and eastern equatorial Pacific, and the Niño 3.4 index is slightly negative. The equatorial Pacific sub-surface temperatures are near average.

The observations, ENSO model forecasts, and the latest CPC/IRI ENSO forecast issued August 8th, all suggest ENSO-Neutral conditions are likely to continue through August-October. For this period, the CPC/ IRI forecast indicates a 73% chance of ENSO-neutral, a 19% chance of La Niña, and only an 8% chance of El Niño.

3. Multi-decadal fluctuations in Atlantic hurricane activity

Atlantic hurricane seasons exhibit extended periods lasting decades (25-40 years) of generally above-normal or below-normal activity. These multi-decadal fluctuations in hurricane activity result almost entirely from differences in the number of hurricanes and major hurricanes forming from tropical storms that first develop in the MDR.

The current high-activity era began in 1995 (Goldenberg et al. 2001). Hurricane seasons during 1995-2012 have averaged about 15 named storms, 8 hurricanes, and 4 major hurricanes, with an ACE value of 151% of the median. Also, the continental U.S. has averaged almost 2 landfalling hurricanes per year during this period. NOAA classifies 12 of the 18 seasons since 1995 as above normal, with eight being very active (i.e. hyperactive). Only two seasons since 1995 were below normal (1997 and 2009, which were both El Niño years).

This high level of activity contrasts sharply to the low-activity era of 1971-1994 (Goldenberg et al. 2001), which averaged only 9.5 named storms (which includes likely under-counts prior during 1971-1980, Landsea et al. 2010), 5 hurricanes, and 1.5 major hurricanes, with an ACE index of 74% of the median. One-half of the seasons during this period were below normal, only two were above normal (1980, 1989), and none were hyperactive. Also, the average number of landfalling hurricanes during this period (1.3) was almost 50% lower than that observed during 1995-2012 (1.9).

Within the MDR, the atmospheric circulation anomalies that contribute to these long-period fluctuations in hurricane activity are strongly linked to the Tropical multi-decadal signal (Bell and Chelliah 2006), which incorporates the warm phase of the AMO and an enhanced west African monsoon system. A change in the phase of the tropical multi-decadal signal coincides with the transition in 1995 from a low-activity era to the current high-activity era.

http://www.cpc.ncep.noaa.gov/products/o ... cane.shtml