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2019 Hurricane Season Forecast #535542
03/25/19 05:43 AM
03/25/19 05:43 AM
Joined: Oct 1999
Posts: 61,687
oregon, spr
Marty Offline OP

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Marty  Offline OP

2019 Atlantic, Caribbean & Gulf Of Mexico Hurricane Season Forecast

Summary: Activity during the 2019 Atlantic Hurricane Season is likely to be influenced by building El Nino conditions. This potentially means a lower than average number of storms, HOWEVER, this does not necessarily mean that the threat for a tropical storm or hurricane impact is lower as there is data supporting the idea of at least one landfall of a tropical storm/hurricane on the US coast and/or eastern Caribbean this season.

In addition, I am expecting the formation of at least one tropical storm in the western Atlantic during either May or early June. In addition, I also think that we could start out “quick” with tropical storm/hurricane formation from May to August, but then slow down in activity during September with the hurricane season potentially ending early in October as El Nino strengthens and attempts to make the Atlantic increasingly more unfavorable for development.

The Numbers: 10 Named Storms, 6 of those storms becoming Hurricanes and 3 of those hurricanes becoming Major Hurricanes (Category 3 or higher on the Saffir-Simpson scale).

Accumulated Cyclone Energy (ACE) Index Forecast: I am forecasting an ACE index this year of 95. This number basically says that I expect that overall activity in the Atlantic may be slightly below average.

ENSO Conditions: The current ENSO state across the Pacific is somewhat similar to what we had during this time in 2015 with weak El Nino conditions occurring right now. Pretty much all of the ENSO model guidance are forecasting somewhere between a weak El Nino and a moderate El Nino throughout this entire year. One big question is whether we will end up seeing a strong El Nino develop at some point this year like we saw in 2015. Unfortunately, the model guidance are not very good at this time of year in determining how strong of a El Nino occurs.

I think that, at the minimum, we will see a weak El Nino persist throughout the rest of this Spring with a moderate El Nino potentially developing this Summer and persisting through the end of 2019. With that said, ENSO forecasts this time of year can be highly inaccurate as has been demonstrated the last few years.

Sea Surface Temperatures: Sea surface temperatures along and south of 20 North Latitude are cooler than average with warmer than average sea surface temperatures occurring north of 20 North Latitude and especially north of 25 North Latitude. If this sort of ocean signal continues (cooler than average tropical ocean temps and warmer than average temperatures outside of the tropics), it could mean a “quiet” season across the Main Development Region with most of the activity occurring outside of the deep tropics.

One of the keys in determining how active/inactive the hurricane season will be is how much will the deep tropics (south of 25 North Latitude) warms up during April, May and June. It should be noted that at this time in both 2017 and 2018, the Atlantic Main Development Region was running a little below average in sea surface temperatures, but this pattern reversed during the hurricane season leading to a much more active season than what was originally thought.

I think that it is quite possible that the deep tropics will end up seeing near average to slightly above average ocean water temperatures during July, August and September. With that said, I think that it is unlikely that this region of the Atlantic will be as warm or as active as it was during 2017 and 2018.

Further north, the ocean water temperatures from the Bahamas to near the US East Coast and into the Gulf of Mexico may remain above average throughout the 2019 Hurricane Season. This could potentially mean we could see tropical systems forming close to the US coastline and the Bahamas.

Analog Years: These are the analog years that seem to be a close match right now to what this hurricane season may be like. They are 1953, 1955, 1961, 1963, 1969, 1976, 1977, 1984, 1986, 1990, 1993, 1997, 1999, 2014 & 2015.

Wind Shear Forecast:
A majority of the seasonal model guidance are forecasting above average wind shear across the Caribbean as well as across the region from the Lesser Antilles to the coast of Africa. In addition, a majority of the model guidance are forecasting near average to below average wind shear values across the Gulf of Mexico as well as across the area of the Atlantic north of 20 North Latitude. What this means is that conditions may be more favorable for development for systems as they move out of the deep tropics and towards the Gulf of Mexico and towards the Bahamas, Bermuda and the US East Coast leading to in-close development.



Risk Areas: The geographic areas I am most concerned about for the 2019 Atlantic Hurricane Season are the Yucatan Peninsula and Belize, the Lower Texas Coast, the Central US Gulf Coast & Coastal North Carolina.

Mid-Atlantic States, Long Island & New England: Even though I am quite concerned about a tropical storm/hurricane impact for coastal North Carolina this season, there is enough evidence in the data, including the analog years & weather pattern that suggests any tropical system could easily be guided right up the entire US East coast instead leading to impacts along the Mid-Atlantic coast and across Long Island and parts of New England. With that said, there isn’t quite enough evidence yet that suggests its a significant threat as of yet.

Coastal North Carolina:
I have significant concerns for a tropical storm or hurricane impact across coastal North Carolina based on the analog data as well as some of the model guidance. The UKMET seasonal guidance, which did very well last year, is forecasting an enhanced threat for a tropical system this season. In fact, this same guidance also seems to hint at any system moving from south to north across eastern North Carolina before being steered away to the east before reaching Long Island and New England.

South Carolina, Georgia, Florida & The Eastern & Northeastern US Gulf Coast: Even though the longer range model guidance seems to suggest otherwise, there are quite a few analog points that indicate the west coast of Florida may be at some threat this season. With that said, I’m not convinced its a significant threat as of yet.

The Central Gulf Coast: The central Gulf coast from southeastern Louisiana to the western Florida Panhandle could be at risk from a tropical storm or hurricane impact. It seems this region of the Gulf Coast is at more risk of a landfall during a El Nino year over a non El Nino year.

The Western Gulf Coast has some risk from a tropical storm or hurricane impact this year with the highest risk of this occurring during the early part of the season. This is supported by the UKMET seasonal model which hints at a enhanced threat during June and July and the fact that a few of the analog years saw at least a threat, if not an impact from a tropical storm or hurricane.

The Central & Eastern Atlantic from the Lesser Antilles to the coast of Africa could end up being less active than it was during 2017 and 2018. It appears quite possible that a ribbon of above average wind shear may set up from the Caribbean to the coast of Africa leading to systems having a hard time developing.

With that said – there are signals in the UKMET seasonal model that suggests the southeastern Caribbean, the Windward Islands and Barbados could see a threat during August and September. Even more curious is that some of the analog data do point to some sort of tropical threat across the Leeward Islands and the Virgin Islands.

Even though I am not placing the Lesser Antilles in a threat area right now, I do think that this region will need to be monitored closely for any tropical threats.

The Caribbean is an area that could be inactive this season due to above average wind shear.



All-in-all, the area of main concerns this season will be for tropical systems forming outside of the deep tropics north of 20 North Latitude and also in the Gulf of Mexico with the 3 main areas of impact concern being coastal North Carolina, the lower Texas coast and the central US Gulf coast.

Finally, we will begin sending out daily tropical weather discussions for the 2019 Atlantic Hurricane Season on Wednesday, May 1st.

2019 Atlantic Tropical Cyclone Names:
Andrea
Barry
Chantal
Dorian
Erin
Fernand
Gabrielle
Humberto
Imelda
Jerry
Karen
Lorenzo
Melissa
Nestor
Olga
Pablo
Rebekah
Sebastien
Tanya
Van
Wendy

Crown Weather


Re: 2019 Hurricane Season Forecast [Re: Marty] #535710
04/05/19 05:34 AM
04/05/19 05:34 AM
Joined: Oct 1999
Posts: 61,687
oregon, spr
Marty Offline OP

.
Marty  Offline OP

CSU 2019 Atlantic Hurricane Season Forecast: Slightly Below-Average

A slightly below-average Atlantic hurricane season is likely in 2019, said the hurricane forecasting team from Colorado State University (CSU) in their latest seasonal forecast issued April 4. Led by Dr. Phil Klotzbach, with coauthors Dr. Michael Bell and Jhordanne Jones, the CSU team called for an Atlantic hurricane season with 13 named storms, 5 hurricanes, 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 80. The long-term averages for the period 1981 - 2010 were 12 named storms, 6.5 hurricanes, 2 intense hurricanes, and an ACE of 92. The CSU outlook also predicted the odds of a major hurricane hitting the U.S. were about 48% (the long-term average is 52%). They gave a 28% chance for a major hurricane to hit the East Coast or Florida Peninsula (the long-term average is 31%), and a 28% chance for the Gulf Coast (the long-term average is 30%). The Caribbean was forecast to have a 39% chance of seeing at least one major hurricane (the long-term average is 42%).

“We have a lot of warmth in the subtropical Atlantic,” said Klotzbach in a livestreamed presentation Thursday from the National Tropical Weather Conference. As a result, Klotzbach said, he expects a relatively large number of weaker storms with subtropical elements, much like 2018, which set the Atlantic record for the largest number of storms (seven) that were subtropical during at least one point in their lives. This is one reason why CSU is predicting a near-average number of named storms but a lower-than-average number of hurricanes and ACE.

The CSU forecast has previously used only statistical techniques to make their forecasts. But this year, they collaborated with the Barcelona Supercomputing Center to use output from the ECMWF (European) model to augment the statistical technique. They used the European long-range ocean/atmosphere model to predict July 2019 conditions, which were then put into the statistical model. The warm sea-surface temperatures projected by statistical-dynamical models for hurricane season prompted Klotzbach and colleagues to bump up the number of named storms from the number predicted by the CSU statistical technique.

Departure of SST from average
Figure 1. Departure of sea surface temperature (SST) from average for April 3, 2019. SSTs in the hurricane Main Development Region (MDR) between Africa and Central America were near-average to slightly below-average. Virtually all African tropical waves originate in the MDR, and these tropical waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present). Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely. Image credit: tropicaltidbits.com.

Analogue years

Five years with similar pre-season February and March atmospheric and oceanic conditions were selected as “analogue” years that the 2019 hurricane season may resemble. These years were characterized by weak to moderate El Niño conditions during August-October, and near-average sea surface temperature (SST) in the tropical Atlantic:

1969 (18 named storms, 12 hurricanes, and 5 intense hurricanes)
1987 (7 named storms, 3 hurricanes, and 1 intense hurricane)
1991 (8 named storms, 4 hurricanes, and 2 intense hurricane)
2002 (9 named storms, 4 hurricanes, and 2 intense hurricanes)
2009 (9 named storms, 3 hurricanes, and 2 intense hurricanes)

The average activity for these years was 13 named storms, 5 hurricanes, 2 major hurricanes, and an ACE of 80—not far from the long-term average. The most notable storms during these years were Hurricane Camille of 1969, which made landfall as a Category 5 storm in Mississippi; Hurricane Emily of 1987, which made landfall in the Dominican Republic as a Category 3 storm;  Hurricane Bob of 1991, which made landfall as a Category 2 storm in New England; and Hurricane Lili of 2002, which made landfall as a Category 1 storm in Louisiana.

SSTs
Figure 2. Departure of SST in the tropical Atlantic Main Development Region (10 - 20°N, 60 - 20°W) plotted for the average of various Atlantic hurricane season types from 1982-2016. Also plotted are 30-day running averages of SSTs for 2017, 2018 and 2019. So far, 2019 is tracking in line with below-average Atlantic hurricane seasons in previous years. However, there is very little spread between below-average, average and above-average hurricane seasons at this time of year. Image credit: Colorado State University (CSU), from their latest seasonal forecast issued April 4.

A weak El Niño and near-average tropical Atlantic SSTs expected

The CSU team cited two main reasons why this may be a slightly below-average hurricane season:

1) The current weak El Niño event in the Eastern Pacific appears likely to continue and perhaps strengthen during the summer/fall. If El Niño conditions are present this fall, this would tend to favor a slower-than-usual Atlantic hurricane season due to an increase in the upper-level winds over the tropical Atlantic that can tear storms apart (higher vertical wind shear).

Sea surface temperatures (SSTs) were about 0.7°C above average during the past month in the so-called Niño 3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 0.5°C above average for five consecutive months (each month being a 3-month average) for a weak El Niño event to be declared (and atmospheric conditions must also be consistent with El Niño). In their latest March 14 monthly advisory, NOAA's Climate Prediction Center (CPC) predicted that the current weak El Niño event has a 60% chance of continuing into the summer. The Australian Bureau of Meteorology, which uses a more stringent threshold than NOAA for defining El Niño, does not recognize that an El Niño event is underway. In the April 2 installment of its biweekly report, the Bureau said that the atmosphere has yet to “show a consistent El Niño-like response”, but maintained their El Niño alert, with a 70% chance of an El Niño developing later this year. The Bureau requirement for an El Niño is for sea-surface temperatures in the Niño3.4 region of the tropical Pacific to be at least 0.8°C above average, vs. the NOAA benchmark of 0.5°C above average.

Among the latest predictions from a large number of statistical and dynamical El Niño models for the peak of the Atlantic hurricane season in August-October, about 1/3 of the models called for neutral conditions, about 2/3 called for El Niño conditions, and none predicted La Niña conditions.

2) The tropical Atlantic is slightly cooler than normal, while the subtropical Atlantic is quite warm, and the far North Atlantic is anomalously cool. The anomalously cool sea surface temperatures in the far North Atlantic suggest that the Atlantic Multidecadal Oscillation (AMO) is in its negative phase. A positive AMO is typically linked with above-average Atlantic hurricane activity; a negative AMO is typically associated with below-average activity.

As always, the CSU team included this standard disclaimer:

"Coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them. They should prepare the same for every season, regardless of how much activity is predicted."

Forecast skill
Figure 3. Comparison of the percent improvement in mean square error over climatology for seasonal hurricane forecasts for the Atlantic from NOAA, CSU and Tropical Storm Risk (TSR) from 2003-2018, using the Mean Square Skill Score (MSSS). Values less than zero indicate that pure climatology does a better job than the forecast. The figure shows the results using two different climatologies: a fixed 50-year (1951 - 2000) climatology, and a 10-year 2009 - 2018 climatology. Skill for forecasts issued in December and April is close to zero, is modest for June forecasts, and is moderate-to-good for August forecasts. Using this methodology, TSR has had the best seasonal forecasts. Image credit: Tropical Storm Risk, Inc. (TSR).

April hurricane season forecasts have little or no skill

On average, April forecasts of hurricane season activity have had no skill (Figure 3), since they must deal with the so-called "spring predictability barrier." April is the time of year when the El Niño/La Niña phenomenon commonly undergoes a rapid change from one state to another, making it difficult to predict whether we will have El Niño, La Niña, or neutral conditions in place for the coming hurricane season. Last year’s CSU April forecast called for a slightly above-average Atlantic hurricane season for 2018, with 14 named storms, 7 hurricanes, 3 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 130. This forecast ended up being successful, as the season actually had 15 named storms, 8 hurricanes, 2 major hurricanes, and an ACE of 129.

The next CSU forecast, due on June 4, is worth paying more attention to. Their late May/early June forecasts have shown considerable skill over the years. NOAA issues its first seasonal hurricane forecast for 2019 in late May, with an update in August.

TSR Atlantic hurricane season forecast due out Friday, April 5

The first forecast for the 2019 Atlantic hurricane by British private forecasting firm Tropical Storm Risk, Inc. (TSR) is due out April 5.

Jeff Masters



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