# Presentation: 206661

## Prospects for subseasonal forecast of Tropical Cyclone statistics with the CFS

- Augustin Vintzileos(1)(3) , Tim Marchok(2) and Hua-Lu Pan(3)
- (1) SAIC (2) GFDL (3) EMC/NCEP/NOAA

## During the period between 2002 – 2006 there were no major ENSO events to dominate climate signals (weak El Ninos occurred in 2002-2003 and 2004-2005 seasons)

- During the same period two interesting episodes occurred in the tropical Atlantic: August 2002 was a quite period in respect to Tropical Cyclones (though September 2002 was very active) in contrast to August 2005 which was very active (as with the whole season of 2005)
- The simple question that we are asking the CFS is:
- Can the CFS predict the anomalies which occurred in the Atlantic ocean in August 2002 and 2005 in one month in advance?

## August 2002 (a calm period) 	vs. August 2005 (a vigorous season)

- August 2002 (a calm period) 	vs. August 2005 (a vigorous season)

- GPCP Observed Precipitation Anomalies (base mean period 2002 – 2006)

- Observed name Tropical Storms

## Outline:

-  Possible sources – not necessarily orthogonal -- of subseasonal predictability for tropical Atlantic Tropical Cyclones and the capacities of the CFS to predict them:
-   The Madden-Julian Oscillation
-   Activity in the Sahel
-   Tropical Atlantic SST
-   Subseasonal (monthly) forecast of the number of occurrence of Tropical Cyclones in the tropical Atlantic in August 2002 - 2006
-   Conclusions and work to follow

## Predicting the MJO may help with prediction of Tropical Cyclone statistics at subseasonal lead times 

- Predicting the MJO may help with prediction of Tropical Cyclone statistics at subseasonal lead times
- This is an idea reflected in published work e.g.:
- 				Maloney and Hartmann, Science, 2000
- 				Mo, Monthly Weather Review, 2000
- 				Higgins and Shi, Journal of Climate, 2001

## IR Temperatures (K) / 200-hPa Velocity Potential Anomalies

- _IR Temperatures (K) / 200-hPa Velocity Potential Anomalies_

- Large scale subsidence reduces the probability for organized convection

- Large scale ascendance increases the probability for organized convection

- Forecasting probabilities for enhanced or suppressed convection at subseasonal lead times due to MJO

## Forecasting probabilities for enhanced or suppressed convection at subseasonal lead times due to MJO 

- Large scale subsidence

- Large scale ascendance

- Forecasting probabilities for enhanced or suppressed convection at subseasonal lead times due to MJO

- _September 7__th_: Large scale subsidence over Atlantic

- _October 4__th_: Large scale ascendance over Atlantic

## Are there any other potential sources of subseasonal predictability for Tropical Cyclone statistics?

**Gray, Science, 1990**
**Landsea *****et al*****., Journal of Climate, 1992**
**Bell and Chelliah, 2006**

- Activity in West Africa during the Monsoon Season

## Snapshot at 5:30 pm EST June 26th, 2008

- Snapshot at 5:30 pm EST June 26th, 2008

- The** GFS **claims that this will be the next Atlantic T.C.  Seems much better organized this evening than it was this morning. We have traced it back to Darfur

## And the last but not least source for subseasonal predictability of T.C. is SST:  

- And the last but not least source for subseasonal predictability of T.C. is SST:

## The issues:

- Is the CFS an adequate tool for predicting the MJO?
- How well is the CFS forecasting the Sahel weather statistics at subseasonal lead times?
- How well is the CFS doing with tropical Atlantic SST forecasts at subseasonal lead times?
- Can the CFS forecast statistics of Tropical Cyclones at subseasonal lead times?

## Retrospective forecast design (CTB experiments):

**Retrospective forecast design ****(CTB experiments)****:**

- Initial conditions:
***Atmosphere, Land*****:** from **Reanalysis 2 (CDAS2)** and from **GDAS (operational atmospheric analysis)**
***Ocean*****:** from  GODAS

- May 23rd to August 11th from 2002 to 2006
- 1 forecast every 5 days, with additional re-forecasts at the beginning of each month
- Forecast lead: 60 days

- Model resolution:
***Atmosphere*****:** T62      =      200Km  x  200Km
-                        T126    =      100Km  x  100Km
-                        T254    =      50Km    x   50Km
***Ocean*****:** the standard CFS resolution

## Skill for the TIO mode (verification CDAS2)

- Skill for the TIO mode (verification CDAS2)

- Persistence forecast

**GDAS**

**CDAS2**

**GDAS**

- Skill up to 14 – 18 days

## Pattern correlation as a function of initialization day and lead time 

- Pattern correlation as a function of initialization day and lead time

- Persistence forecast cannot capture transitions

- CFS forecast captures well some transitions but not well other ones

- August 5th

- June 8th

- June 8th

## Longitude – height Equatorial section 

- 200 hPa

- 850 hPa

- Longitude – height Equatorial section

## Longitude – height Equatorial section 

- 200 hPa

- 850 hPa

- Longitude – height Equatorial section

**Maritime Continent**

## Longitude – height Equatorial section 

- 200 hPa

- 850 hPa

- Longitude – height Equatorial section

**Maritime Continent**

## Longitude – height Equatorial section 

- 200 hPa

- 850 hPa

- Longitude – height Equatorial section

## Longitude – height Equatorial section 

- 200 hPa

- 850 hPa

- Longitude – height Equatorial section

**Maritime Continent**

## The operational CFS as a tool for forecasting cumulative precipitation anomalies at subseasonal lead times over the Sahel 

- The operational CFS as a tool for forecasting cumulative precipitation anomalies at subseasonal lead times over the Sahel
- (Vintzileos and Thiaw, 2006)

## Thick Black Line: Anomaly correlation (CFS vs. CMAP)

**For initializations from May 9-13 to July 30 – August 3**

*Initialization issues? ****YES!!**** M*ore details will be shown at Wednesday’s Climate Test Bed session

*No seasonal skill*

*Subseasonal skill*

*Forecast with AR(1) precipitation*

## A lagged 14-ensemble member monthly forecast for August 2002 – 2006 initialized by Reanalysis 2 and GDAS in July 2, 3, 5, 6, 9,10, 12 

- A lagged 14-ensemble member monthly forecast for August 2002 – 2006 initialized by Reanalysis 2 and GDAS in July 2, 3, 5, 6, 9,10, 12

- July

- August

- In what follows we are using the tracking system that was developed at NCEP by Tim Marchok (Marchok 2002) for each ensemble member and then combine the number of detected T.C. to produce a density field (number of T.C. per given area).

- From what was presented above, both the ensemble generation technique (lagged ensemble) and the distance from the target makes the MJO a not very possible candidate for forecast of T.C. activity

## August Climatology

- Model x 10

- OBS

## Comparing the observed and forecast sources of predictability for August 2002 and 2005:

- (1) SST
- (2) MJO
- (3) Conditions over the Sahel

## SST

## Observations

- Forecast

- The CFS is doing an excellent work forecasting the tropical Atlantic SST at lead times of one month

## MJO

## Atlantic

- 2002 not an active year (Atlantic)

- 2005 a very active year (Atlantic)

- divergence

- Upper level convergence =
- decreased chances for convection

- convergence

- Projection of 20S-20N averaged Zonal wind at 200hPa to the MJO mode during August 2002 and 2005

- Upper level divergence =
- Increased chances for convection

## Forecasting the MJO for August 2002 and 2005 from early July

- Forecast MJO for August 2002

- Forecast MJO for August 2005

## Forecast of activity over the Sahel

## August 2002 – a month of weak T.C. activity

## August 2005 – a month of strong T.C. activity

## Forecast of anomalous occurrence of Tropical Cyclones

- 2002 an inactive season

- 2005 a very active season

- T62

- T126

- T254

- Blue = less occurrences than normal

- Red = more occurrences than normal

## Conclusions(I):

- The CFS manages to produce an August climatology of occurrence of Tropical Cyclones which is realistic in the tropical Atlantic. Work has to be done in order to improve the results and especially understand the drawbacks noticed in the eastern Pacific.
- The CFS is a good tool for the forecasts of anomalous low and high occurrence of Tropical Cyclones in years 2002 and 2005. This is a promising result and work will be done using the new CFSRR hindcast database in order to extend these findings to more cases including more active ENSO years.
- Reasons for these good forecasts include (1) Skillful forecast of weather statistics at subseasonal lead times over the Sahel, (2) good forecasts of the tropical Atlantic SST at 1-2 month lead time and (3) a skillful forecasts of the MJO  depending on its phase – a real solution to the Maritime Continent Barrier will certainly improve these forecasts.
- Work on ensemble generation techniques addressing the subseasonal lead times is considered under the CTB

## Conclusions (II)

- We have notice a better simulation of the mean climate as the resolution increases to T254, at a first glance it seems that this improvement is not affecting forecasts. However, more studies have to be conducted towards this direction as the new CFSRR will run at T126. Studies of downscaling from T126 to T254 or higher should be done.

## Mean August (2002 – 2006) differences due to horizontal resolution

- Precipitation

- Number of T.C. occurrences

- The northward shift in T.C. occurrences also appears in precipitation and extends all across Africa

## 2003 not an active year (correct forecast)

## 2004 an active year in the west Atlantic

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