# Presentation: 782098

## Tropical Cyclone QPF

- David Roth
- NOAA Hydrometeorological Prediction Center
- Camp Springs, MD

- March 22, 2006

## Rainfall forecasts from landfalling TC’s

- _standard forecasting tools_

-  Local Tropical Cyclone Rainfall Climatology
-  GFS/NAM/GFDL precipitation forecasts
-  r-CLIPER  (Climatology based on 1st order stations)
-  TRaP  (persistence to capture structure/Day 1)

- _standard validation tools_

-  bias score
-  equitable threat score

## Factors impacting rainfall distributions in landfalling TC’s

- Storm size
- Topography
- Nearby synoptic-scale features
- Time of day – core rainfall overnight/ outer band rainfall during daylight

## Percent of Maximum storm total rainfall (Hrs)81 cases – 1991-2005

**   ****0.92  1.40  1.76  2.04  2.98   3.61   5.01  6.71   9.77  11.48 12.34  13.34**
-   1.90  3.04  4.56 6.08 10.04  13.47 22.27 28.33 32.52 35.29 36.31 40.68

- Average
- Maximum

## Picking an analog for a TC event

- Size is important...look at the current rain shield and compare it to storm totals from the past
- Is/was there vertical wind shear in current and past events?
- Look for storms with similar/parallel tracks
- Is topography/prism data a consideration?
- Look for fronts in the vicinity for current and possible analogs
- Not all TC events will have a useful analog

## Isbell (1964) vs. Wilma (2005)

## Isabel (2003) vs. Fran (1996)

## Production of TC QPF

-   ***Forecasts made in six-hourly increments from Hour 12-84 ***
***   ******and in one 48 hour chunk for Hours 84-132 twice a day by***
***   ******3 forecasters (Day 1, Day 2/3, and Medium Range temps/pops)***
-   Start With Model Closest to TPC Forecast (usually GFS)
-   Locate relevant synoptic scale boundaries/coastal front
-   Use conceptual models/current structure to modify/shift QPF
-    (TRaP and recent satellite/radar imagery for current structure)
-   Look at storm-relative shear/H2 winds to further shift/limit QPF
-   Use climatology (PRISM, r-CLIPER, TC Rainfall Climatology) to:
-      Temper down forecast bias/act as a reality check
-      Depict areas of terrain that could be significantly impacted
-      Help Create TC rainfall statements for the Public Advisories
-   Forecasts issued at by 06/18z (Days 1-3) and 12z/0z (Days 4-5 and
-     5-day accumulation graphic)

## QPF Equitable Threat Score

## TC Model Track Error (km) (2003-2005)

- GFDL: 71.5 110.8 145.9 183.7 276.2 383.5
-             512.5
- GFS:  78.1 117.6 155.6 202.1 289.5 460.5 580.2
- UKMET: 89.3 137.3 180.1 220.7 295.2 463.0 556.8
- NAM:  96.7 167.0 236.4 302.3 410.9

## Maximum Potential Equitable Threat Score improvements due to shifting grid

## Dependence on TPC track - Rita

- Threat/Bias for 5 Day QPF

- September 21/12z Forecast
- 0.25 .453 1.52 H G .498 1.39
- 0.50 .350 1.46 H G .414 1.35
- 1.00 .197 .961 H G .258 1.24
- 2.00 .030 .725 H G .168 .858
- 3.00 .013 1.28 H G .093 1.06
- 4.00 .009 2.61 H G .069 1.86
- 5.00 .000 3.49 H G .021 3.01
- 6.00 .000 4.23 H G .018 4.69
- September 22/12z Forecast
- 0.25 .536 1.33 H G .541 1.08
- 0.50 .468 1.18 H G .534 .978
- 1.00 .367 1.07 H G .366 .781
- 2.00 .164 .777 H G .234 .792
- 3.00 .163 1.35 H G .224 .916
- 4.00 .128 2.50 H G .199 1.63
- 5.00 .090 3.74 H G .174 2.18
- 6.00 .090 5.71 H G .161 2.98

## Model Forecast Biases/Verification relating to TC QPF

## Pattern comparisons for U.S. landfalling stormsFrom Rogers, Black, Marchok, 2005 IHC

- Equitable Threat Score

- Pattern comparisons for U.S. landfalling stormsFrom Rogers, Black, Marchok, 2005 IHC

## QPF Skill – Core Rainfall (1998-2004)From Rogers, Black, Marchok, 2005 IHC

## Summary comparison for all modelsFrom Rogers, Black, Marchok, 2005 IHC

## Summary comparison for all models (cont.)

## Cindy, Dennis, Katrina, Ophelia, Rita, & Wilma – Threat Scores

## Cindy, Dennis, Katrina, Ophelia, Rita, & Wilma - Bias

## Coming Attractions

- Growing TC rainfall climatology online; to additional mesonet rainfall information being included (i.e. Chester County PA, MA)
- New r-CLIPER to account for topography and shear for 2006
- Operational model improvements (ECMWF 1/06, GFS/NAM upgrades continue)
- New Models (WRF)