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Tropical Storm Email List http://tstorms.org/

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Tropical-Storms is a mailing

list only for those who are

professionally active in either

the research or forecasting of

tropical storms worldwide.

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those who are professionally

active in the research or

forecasting of monsoons

worldwide.

Tropical Cyclogenesis:

Operational Forecasting Perspective

International Workshop on Tropical Cyclones

Jeju Island, South Korea

Working group: Chris Landsea (RSMC Miami), Lixion Avila

(RSMC Miami), Thierry Dupont (RSMC La Reunion), S. D.

Kotal (RSMC New Delhi), and M. Mohapatra (RSMC New

Delhi)

Accurate tropical cyclone genesis

forecasting is important because of

• The need to provide extended community response

planning, especially in remote or large communities

• The need to provide advisories at extended forecast

ranges for offshore and onshore commercial activities

• The requirement for National Meteorological Services to

manage forecasting and reconnaissance resources

• The potential to reduce future track, intensity, and size

errors by more accurately defining the likely genesis

location

Within the 2010 IWTC report there was a substantial optimism that genesis forecasting was

becoming a solvable problem:

• Both Ensemble Prediction Systems (EPS) and deterministic

Numerical Weather Prediction (NWP) models were routinely

capturing TC formation.

• Improvement in formation forecasts from operational numerical

models were expected given advances in various aspects of

numerical weather prediction systems, which includes increased

resolution, improved parameterization schemes, and improved use

of observations, especially satellite data to improve initial

conditions.

• However, tropical cyclone genesis forecast continued to remain a

challenging aspect of operational forecasting in the major tropical

forecasting centers, as there was still no effective systematic

approach in place for genesis forecasting, especially with respect to

NWP guidance.

conditions.

NWP guidance.

conditions.

NWP guidance.

Definition of Tropical Cyclone

“A warm-core, non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and closed surface wind circulation about a well-defined center.”

- RSMC Miami/Honolulu (Atlantic/Northeast and North Central Pacific)

NOTE: No lower bound of sustained winds

Various Definitions of Tropical Cyclone

• RSMC La Reunion (Southwestern Indian Ocean) -the maximum of the average wind speed has to be at least 28 kt before a tropical disturbance can be considered a tropical depression.

• RSMC New Delhi (North Indian Ocean) - 17 kt.

• RSMC Fiji and TCWCs of the Southeastern Indian Ocean and Southwestern Pacific Ocean) - 34 kt.

• RSMC Tokyo (Northwest Pacific Ocean)- has no lower bound wind speed threshold

Forecasting Genesis when

Definitions Differ • Makes intercomparison of

genesis across basins

problematic

• Decision of if/when

genesis occurs remains

subjective

• Role of human forecaster

is crucial for genesis

prediction

• Makes intercomparison of

genesis across basins

problematic

• Decision of if/when

genesis occurs remains

subjective

• Role of human forecaster

is crucial for genesis

prediction Genesis of Phanfone,

18W, 2014

Genesis Predictions

• Observations and Analyses

• Statistical Approaches

• Deterministic Global Models

• Ensemble Prediction Systems

• Statistical-Dynamical Hybrid Approaches

Genesis Predictions

Genesis Forecasting:

Observations and Analyses

A pre-existing disturbance containing

abundant deep convection

• Latitudes poleward ~5o

• SST > 26oC

• A “sufficiently” unstable atmosphere & deep layer of moist air

Genesis Forecasting:

Observations and Analyses (cont.)

Small vertical shear of the horizontal wind

Upper-tropospheric anticyclonic outflow

Enhanced lower tropospheric relative vorticity

Appearance of curved banding features in the deep convection

Falling surface pressure: 24-hour pressure changes (falls) of usually 3 mb or more

Genesis Predictions

Cossuth et al. (2013) moe.met.fsu.edu/genesis

Tropical

Cyclone

Formation

Probability

Schumacher

et al. (2009)

http://www.ssd.noaa.gov/PS

/TROP/TCFP/index.html

24-48h

Genesis Predictions

Examining Global Model Output

for Genesis

• At least one closed isobar (at 4 mb interval) with

lowered central pressure

• Reasonable structure (closed circulation center,

warm core, deep vertical extent, non-baroclinic)

• Longevity of the vortex for at least a day

Very Good Global Model Predictions of Genesis GFS forecasts verifying at genesis time of Hurricane Arthur

F168 F156 F144 F132 F120 F108 F96 F84 F72 F60 F48 F36 F24 F12 F00

Not so Good Global Model Predictions of Genesis GFS forecasts verifying at genesis time of Hurricane Sandy

Genesis Predictions

GFS Ensemble-based Probabilities of Genesis http://www.emc.ncep.noaa.gov/gmb/tpm/emchurr/tcgen/

Composite track of tropical cyclone before genesis Elsberry et al. (2011a,b)

Genesis Predictions

Tropical Cyclone Genesis Index http://rammb.cira.colostate.edu/realtime_data/nhc/tcgi/

Predictors:

1) Dvorak classification

2) 850 mb divergence

3) 850 mb vorticity change

4) 850-200 mb shear

5) 600 mb humidity

6) Deep convection

Dunion (2013)

Blending deterministic global models for

genesis probabilities Halperin et al. (2013) - http://moe.met.fsu.edu/modelgen/

Blending deterministic global models for

genesis probabilities Halperin et al. (2013) - http://moe.met.fsu.edu/modelgen/

Tropical Weather Outlook

Pre-Genesis Tropical Cyclone

Advisories at RSMC Miami

• To be issued for systems with at least a

medium likelihood of genesis within 48 h

• 72 hr track, intensity, size forecast

• Only to be issued when a Tropical Storm

Warning, Hurricane Watch, or Hurricane

Warning needed

• Beginning in 2016 experimentally

Example of Pre-Genesis Advisory

Possible Recommendations

• Researchers should develop methods for providing quantitative

(probabilistic) genesis prediction guidance via deterministic,

ensemble, and statistical-dynamical models

• Researchers should develop methods for provide methods for

providing pre-genesis prediction guidance of TC track, intensity

and size via deterministic, ensemble, and statistical-dynamical

models

• RSMCs/TCWCs should explore issuing quantitative genesis

predictions to the public

• RSMCs/TCWCs should explore increasing lead-time of existing

quantitative genesis predictions to the public

• RSMCs/TCWCs should explore the possibility of issuing pre-

genesis tropical cyclone track, intensity, and size forecasts

models

Tropical Cyclogenesis:

Operational Forecasting Perspective

International Workshop on Tropical Cyclones

Jeju Island, South Korea

Working group: Chris Landsea (RSMC Miami), Lixion Avila

(RSMC Miami), Thierry Dupont (RSMC La Reunion), S. D.

Kotal (RSMC New Delhi), and M. Mohapatra (RSMC New

Delhi)

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