Montag, 1. Juni 2015

The 2015 Atlantic Hurricane Begins

New CSU, TSR Forecasts Call For a Quiet Season.




 The 2015 Atlantic hurricane season is officially underway. We've already had one early season storm, Tropical Storm Ana; will we have an early June Tropical Storm Bill? There are indications that the second tropical depression of the year has a chance to form late this week in the waters near South Florida or the Bahama Islands on Friday or Saturday. We have warmer than average SSTs in these waters, and the Madden-Julian Oscillation (MJO) is expected to be active in the Western Hemisphere late this week, and both of these factors argue for higher than usual odds of an early June tropical depression forming in the Atlantic. Over the past few days, the GFS model has been consistently advertising the possibility that an area of low pressure capable of developing into a tropical depression will form in this region, although the European model (so far) has not gone along with this idea. If we do get something developing, it would potentially be a heavy rain threat for South Florida and the Northern Bahamas over the weekend, but then move northeastwards out to sea without troubling any more land areas.



 Summary of the 2015 Atlantic hurricane season forecasts
The major hurricane forecasting groups are not impressed with this season's potential to be an active one, and are universally calling for 2015 to be a below average to way below-average year for the Atlantic. The highest forecast numbers were from Weather Underground Community Hurricane Forecast, which called for 11 named storms, 5 hurricanes, and 2 major hurricanes. The lowest numbers were from North Carolina State University: 5 named storms, 2 hurricanes, and 1 intense hurricane. The long-term averages for the past 65 years are 11 named storms, 6 hurricanes, 3 intense hurricanes. Here are the forecasts:

NOAA: 8.5 named storms, 4.5 hurricanes, 1 major hurricane, ACE index 62.5% of normal.
Colorado State University (CSU): 8 named storms, 3 hurricanes, 1 major hurricane, ACE index 44% of normal.
Tropical Storm Risk, Inc. (TSR): 10 named storms, 4 hurricanes, 1 intense hurricane, ACE index 36% of normal.
UKMET office: 8 named storms, 5 hurricanes, ACE index 74% of normal (June - November.)
FSU Center for Ocean-Atmospheric Prediction Studies (COAPS):
Weather Underground Community Hurricane Forecast: 11 named storms, 5 hurricanes, 2 major hurricanes
WSI: 9 named storms, 5 hurricanes, 1 major hurricane
Penn State: 8 named storms.
North Carolina State University: 5 named storms, 2 hurricanes, 1 intense hurricane.
Coastal Carolina University: 8 named storms, 4 hurricanes, 2 intense hurricanes.
The Cuban Meteorological Service, INSMET: 9 named storms, 3 hurricanes.

The main reason for the quiet forecasts is the likely intensification of the current moderate strength El Niño. Every 3 - 7 years, variations in tropical winds and pressure shift warm ocean waters eastwards from the Western Pacific to the South American coast, causing an El Niño event. The unusually warm water tends to drive an atmospheric circulation that brings strong upper-level winds to the tropical Atlantic, creating high levels of wind shear that tend to tear hurricanes apart. Another factor leading to lower forecast numbers than in previous years is the fact that sea surface temperatures in the tropical Atlantic are near average to below average this year--quite a bit cooler than we've seen during the typical year during our active hurricane period that began in 1995.


 Colorado State predicts a below-average hurricane season: 8 named storms
A new Atlantic hurricane season forecast issued June 1 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) again calls for a below-average season with 8 named storms, 3 hurricanes, 1 intense hurricane, and an Accumulated Cyclone Energy (ACE) of 40, which is about 44% of average. The forecast calls for a below-average chance of a major hurricane hitting the U.S., both along the East Coast (15% chance, 31% chance is average) and the Gulf Coast (15% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also below average, at 22% (42% is average.) The June 1 numbers are nearly unchanged from their April 9 forecast, with the exception of an additional named storm (due to the formation of Tropical Storm Ana in May.)

CSU's Analogue years: 1997, 1987, 1982, 1972, 1965, and 1957
The CSU team picked six previous years when atmospheric and oceanic conditions were similar to what they expect for this year: at least moderate El Niño conditions, and generally cool sea surface temperatures in the tropical Atlantic. Those years were 1997 (which featured 8 named storms, 3 hurricanes, and 1 intense hurricane); 1987 (7 named storms, 3 hurricanes, and 1 intense hurricane); 1982 (6 named storms, 2 hurricanes, and 1 intense hurricane); 1972 (7 named storms, 3 hurricanes, and 0 intense hurricanes); 1965, featuring Hurricane Betsy, which hit New Orleans as a Category 3 storm; and 1957, which featured the deadliest June hurricane on record, Hurricane Audrey, which killed 416 people in Texas and Louisiana. The average activity for these years was 7 named storms, 3 hurricanes, and 1 major hurricane.

TSR predicts a below-average hurricane season: 10 named storms
The May 27 forecast for the 2015 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) calls for a below-average season with 10 named storms, 4 hurricanes, 1 intense hurricane, and a remarkably low Accumulated Cyclone Energy (ACE) of 37. The long-term averages for the past 65 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 102. TSR rates their skill level as modest for these late May forecasts: 6 - 24% higher than a "no-skill" forecast made using climatology. They project that 2 named storms will hit the U.S., with 1 of these being a hurricane. The averages from the 1950-2014 climatology are 3 named storms and 1 hurricane hitting the United States. TSR rates their skill at making these May forecasts for U.S. landfalls just 4% - 8% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects one named storm and no hurricanes in 2014. Climatology is 1.1 named storms and less than 0.5 hurricanes.

TSR's two predictors for their statistical model are the forecast July - September trade wind speeds over the Caribbean and tropical North Atlantic, and the forecast August - September 2015 sea surface temperatures (SSTs) in the tropical North Atlantic Main Development Region (MDR) for hurricanes. Their model is calling for SSTs 0.33°C below average and trade winds 1.36 m/s stronger than average during these periods; both of these factors should act to decrease hurricane and tropical storm activity. The July-September 2015 trade wind prediction is based on an expectation of weak El Niño conditions in August-September 2015. TSR will issue an updated forecast on July 6, 2015.

Even a quiet hurricane season can be devastating
Quiet hurricane seasons with below-average activity can still produce major hurricanes that cause massive devastation. The five seasons that CSU lists as analogue years for 2015 produced four hurricanes that had their names retired, including one that killed 8,000 people in Cuba (Flora of 1963) and one that killed over 400 people in Texas and Louisiana (Audrey of 1957.) Even if this is an El Niño year, that doesn't mean it will be a quiet season. Recall the El Niño year of 2004, when four major hurricanes pounded the U.S.--Ivan, Charlie, Jeanne, and Frances. Those of you in Hurricane Alley should prepare for the 2015 season the same way you would for a predicted hyperactive season, and be ready for the Storm of the Century to hit your location.

Good luck to everyone in Hurricane Alley this hurricane season, and I look forwards to tracking all the activity this year with you!

Freitag, 8. Mai 2015

Subtropical Storm Ana

Summary of 800 am EDT...1200 UTC...information
location...31.5n 77.5w
about 170 mi...275 km SSE of Myrtle Beach South Carolina
maximum sustained winds...45 mph...75 km/h
present movement...stationary
minimum central pressure...1005 mb...29.68 inches
Watches and warnings
changes with this advisory:

Summary of watches and warnings in effect:
A tropical storm watch is in effect for...
* Edisto Beach South Carolina to Cape Lookout North Carolina
A tropical storm watch means that tropical storm conditions are
possible within the watch area, generally within 48 hours.
A Tropical Storm Warning could be issued later this morning.
For storm information specific to your area, including possible
inland watches and warnings, please monitor products issued by your
local National Weather Service forecast office.
Discussion and 48-hour outlook
at 800 am EDT (1200 utc), the center of subtropical storm Ana was
located near latitude 31.5 north, longitude 77.5 west. The storm
has been nearly stationary during the past few hours but is expected
to move more toward the north-northwest later today.  A turn
toward the northwest with a slight increase in forward speed is
expected by the weekend.
Maximum sustained winds remain near 45 mph (75 km/h) with higher
gusts.  Some slight strengthening is forecast during the next
day or so.
Winds of 40 mph extend outward up to 160 miles (260 km) from the
The minimum central pressure reported by an Air Force Reserve
reconnaissance unit aircraft is 1005 mb (29.68 inches).
Hazards affecting land

wind: tropical storm conditions are possible within the watch area
by Saturday afternoon or evening.
Storm surge: the combination of storm surge and the tide
will cause normally dry areas near the coast to be flooded by rising
waters. The water could reach 1 to 2 ft above ground within the
watch area if the peak surge occurs at the time of high tide.
For information specific to your area...please see products issued
by your local National Weather Service office for more details.
Rainfall: Ana is expected to produce rainfall accumulations of 2 to
4 inches over eastern portions of North Carolina and South Carolina
through the weekend.
Surf: swells generated by Ana are affecting portions of the
southeastern U.S. Coast.  These swells are likely to cause life-
threatening surf and rip currents.

Montag, 1. Dezember 2014

Temporada de huracanes concluye tranquila

La temporada de huracanes de este año en la cuenca atlántica, que terminó ayer domingo, ha sido “relativamente tranquila, tal como se predijo”, y supone nueve años consecutivos sin que un ciclón azote Florida, algo que sí resulta “extraordinario”, resaltó un meteorólogo.

“Ha sido una temporada relativamente tranquila”, pero lo que sí es “sorprendente” es que en los últimos nueve años ningún ciclón haya impactado las costas de Florida. Eso es todo un récord”, dijo Dennis Feltgen, meteorólogo y portavoz del Centro Nacional de Huracanes (CNH), dependiente de Administración Nacional de Océanos y Atmósfera de Estados Unidos (NOAA).

En junio pasado, al comienzo de la temporada, los cálculos de la NOAA preveían una actividad menor de lo normal, con la formación de entre ocho y trece tormentas tropicales, de las cuales entre tres y seis iban a llegar a huracanes, y uno o dos de ellos iban a ser de categoría mayor (3, 4 o 5 en la escala Saffir-Simpson).

El vaticinio fue exacto: hubo ocho tormentas tropicales, de las que seis se transformaron en huracanes

Montag, 6. Oktober 2014

Quietest Atlantic Hurricane Season Since 1986

The traditional busiest month of the Atlantic hurricane season, September, is now over, and we are on the home stretch. Just three weeks remain of the peak danger portion of the season. September 2014 ended up with just two named storms forming--Dolly and Edouard. Since the active hurricane period we are in began in 1995, only one season has seen fewer named storms form in September--1997, with Category 3 Hurricane Erika being the only September storm. Between 1995 - 2014, an average of 4.3 named storms formed in September. With only five named storms so far in 2014, this is the quietest Atlantic hurricane season since 1986, when we also had just five named storms by the beginning of October. In terms of Accumulated Cyclone Energy (ACE), activity in the Atlantic up until October 1 has been only about 43% of the 1981 - 2010 average.

 Tracks of Atlantic named storms in 2014. Note how all of this year's hurricanes (tracks in red) have occurred well north of the tropics, north of 24°N latitude--a testament to how hostile for development conditions have been in the tropics, due to dry, sinking air. Image credit: National Hurricane Center.

 Forecast for the remainder of hurricane season

Looking at climatology, since 1995, we have seen an average of 3.6 named storms form in the Atlantic after October 1. Two of those years--2006 and 2002--saw no storms form after October 1. The most post-October 1 storms was eleven, which occurred in 2005--no surprise there! The latest 2-week forecast from the GFS and European models show a continuation of the basic atmospheric pattern we've seen over the tropical Atlantic this season, with plenty of dry, sinking air. These conditions should lead to lower than average activity into mid-October, which is when historically, Atlantic hurricane activity begins to drop sharply. I expect we'll see at least one more named storm in the Atlantic this year, with two a more likely number. It's unlikely we'll get three or more post-October 1 named storms.

During October, the focus of Atlantic tropical cyclone genesis shifts to the Western Caribbean, Gulf of Mexico, and the waters between the Bahamas and Bermuda. The Lesser Antilles typically see very few tropical cyclones after October 1, and I expect their hurricane season is over. Sea Surface Temperatures over the Caribbean are currently 0.2°C above average, and 0.4°C above average in the Gulf of Mexico.

 Quiet in the Atlantic

A tropical wave predicted to come off the coast of Africa on Saturday is forecast by the UKMET and GFS models to develop by Monday in the vicinity of the Cape Verde Islands. An upper-level trough of low pressure over the Eastern Atlantic will bring high wind shear to this region early next week, though, making developing difficult. Another major invasion of dry air from the Sahara is currently in progress over the Tropical Atlantic, which will make it difficult for any tropical storms to make the crossing from Africa to the Lesser Antilles intact.