Transcript TPC Technical Support Branch Current Priorities and Draft

Topic 4:
Climate Variability and Seasonal
Prediction of Tropical Cyclone
Activity/Intensity
27 November, 2006
IWTC-6 – San Jose, Costa Rica
Chris Landsea
National Hurricane Center, Miami
Topic 4.0: The 2004 and 2005
Atlantic Hurricane Seasons (Max
Mayfield – Rapporteur)
1. Extraordinarily busy for both overall activity
(especially in 2005) and U.S. landfalling
hurricanes (both seasons)
2. The combination of these years in conjunction
with prominent papers published has helped to
push to the forefront for the public issues of
natural climate variability and anthropogenic
climate change with regards to hurricanes.
NOAA Dork Logo
Topic 4.1: Variability of Tropical
Cyclone Activity/Intensity on
Intraseasonal and Interannual Scale
(Chang-Hoi Ho – Rapporteur)
1. Well-established relationships between
Madden-Julian Oscillation and TC activity
(primarily genesis) in most global basins.
2. Also observed are significant intraseasonal
alterations on the order of 10-25 days in
Northwest Pacific – possibly linked to
monsoon trough development/migration.
Topic 4.1: Variability of Tropical
Cyclone Activity/Intensity on
Intraseasonal and Interannual Scale
(Chang-Hoi Ho – Rapporteur)
1. El Nino-Southern Oscillation is dominant interannual
variability factor globally (genesis, intensity, and tracks),
though it is weak in the Indian Ocean.
2. The influence of the stratospheric Quasi-Biennial
Oscillation has been linked to TC activity in three basins,
but is secondary to ENSO.
3. Other phenomenon (e.g., Arctic Oscillation, Antarctic
Oscillation, and North Atlantic Oscillation) have also been
identified in individual basins.
Topic 4.3: Short-term Climate (Seasonal
and Intraseasonal) Predictions of Tropical
Cyclone Activity/Intensity (Suzana
Carmago – Rapporteur)
1. Intra-seasonal tropical cyclone forecasts
– Statistical forecasts
2. Seasonal tropical cyclone forecasts
– Statistical forecasts (whole basin)
– Statistical forecasts (Landfall probability)
– Dynamical forecasts
ENSO SST loop here…
BMRC
Dr. Bill Gray
Colorado State University
Discovered link between
El Nino and Atlantic
Hurricanes in 1984
El Nino versus La Nina
Hurricane Probabilities
El Nino-Southern Oscillation forecasts –
Issued in November 2005
El Nino
La Nina
El Nino-Southern Oscillation forecasts –
Issued in May 2006
Atlantic Seasonal Tropical Cyclone Forecasts for 2006
IRI
Evolution of the 2006 El Nino
NOAA/ESRL
2006 Atlantic Hurricane Season
Weather Underground
El Nino-Southern Oscillation forecasts –
Issued in November 2006
Topic 4.2: Possible Relationships between
Climate Change and Tropical Cyclone
Activity (Tom Knutson – Rapporteur)
1. A century-scale SST increase in Atlantic and Pacific tropical cyclogenesis regions is
likely due in large part to increased greenhouse gases (akin to global mean SST).
2. Several recent studies have found increasing trends in TC intensity and frequency
in individual ocean basins, which have been related to independent SST increases
that are likely due to greenhouse warming. However, there are concerns that data
problems may have greatly affected the TC trend estimates.
3. There is continued debate over the cause of tropical Atlantic SST variability and
multidecadal variability of Atlantic major hurricane activity since the 1940s—in
particular on the relative roles of internal variability (the Atlantic Multidecadal
Oscillation) vs radiative forcing (greenhouse gases, aerosols, volcanoes, etc).
4. Future TC intensity projections: increase in TC intensities is likely (~4 to 5% wind
speed increase per degree Celsius CO2-induced warming is current estimate). A
recent study implies that TC destruction potential could then increase by ~30% per
degree Celsius. Increased rainfall rate from TCs is also likely. There is debate as to
whether changes in TC geographical distribution could increase these sensitivities.
5. Future TC frequency projection: undetermined. Several recent models show global
decreases with increases in a few basins, though confidence in these projections is
low.
Webster et al. (2005)
Coverage Today of Meteorological/Oceanographic Satellites
A globally consistent satellite-based reanalysis of
hurricane intensity trends…
New record
Old record
Kossin et al. (in review)
Excellent agreement in the Atlantic and East Pacific!
Terrible agreement everywhere else!
Kossin et al. (in review)
In Atlantic, the frequency of storms is well correlated with
tropical Atlantic SSTs
Emanuel (2006); Mann and Emanuel (2006)
2005 Hurricane Season
Open Atlantic
Ocean Differences
1933 Hurricane Season
Satellite era 58% strike land
Pre-satellite era 77% strike land
Considerations/Recommendations for Topic
4.1 (Intraseasonal/Interannual Associations)
• Little work has been done on intraseasonal/interannual variations and controls of
tropical cyclone track. There is a big difference in impact between, say, the 1995
and 2004 Atlantic seasons because of steering changes.
• Proposed links of the hemispheric Annual Modes (Arctic Oscillation [including
the North Atlantic Oscillation] and Antarctic Oscillation) to tropical cyclone
activity need better physical foundation than is available currently.
• Near-global relationships have been identified between the stratospheric QBO
and tropical cyclone activity. However, a verified physical connection has not
been identified. Also why has the Atlantic tropical cyclone-QBO relationship
dried up?
• Do western and central Pacific tropical cyclones play a meaningful active role in
El Nino-Southern Oscillation formation/development or merely a passive,
secondary association?
• Is the new hypothesis of El Nino and Atlantic tropical cyclone activity (via
changes in the moist static stability) viable?
Considerations/Recommendations for Topic
4.3 (Intraseasonal/Interannual Forecasting)
• Intra-seasonal operational tropical cyclone forecasts are
beginning to be produced in real-time.
• Verifications and skills for real-time seasonal forecasts
should be made readily available from all forecasts.
• Skill analysis (in hindcasts and real time) should be
published in peer review papers, if possible with a
common metric for all forecasts.
• Improvements could be possible with new homogeneous
datasets for TC (e.g. new dataset by Jim Kossin).
• Combination of statistical and dynamical methods should
be used for improvement in landfall prediction.
• Desperate need for improved forecasting of El NinoSouthern Oscillation.
Considerations/Recommendations for Topic
4.2 (Climate Variability and Change)
• Re-analyses of current tropical cyclone database should be highest
priority, including creative homogeneous record creation (a la
Kossin et al.). This would also include efforts on a more
generalized wind-pressure relationship (e.g., Knaff & Zehr) as well
as better understanding of tropical cyclone wind structure (e.g.,
Kepert, Powell, Franklin, etc.).
• Extension of records farther back in time either from historical
observations (e.g., Perez, Chenoweth, Mock) or via
paleotempestology methods should be strongly encouraged.
• Modeling/theory efforts on the effect of anthropogenic greenhouse
gases should focus upon how tropical cyclone intensity, duration,
frequency can vary both today and in future. Modeling work
should address both the vortices in the model as well as how
environmental fields are altered.
• Continued research into the Atlantic Multidecadal Mode and its
causes are needed to more fully delineate the roles of natural and
manmade forcing.
Topic 4:
Climate Variability and Seasonal
Prediction of Tropical Cyclone
Activity/Intensity
27 November, 2006
IWTC-6 – San Jose, Costa Rica
Chris Landsea
National Hurricane Center, Miami