# Presentation: 329619

## Tropical Cyclone Rainfall

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

- Last Updated November 20, 2008

## Tropical Cyclone 
Rainfall Climatology

- Rainfall Climatology

## Timing of Peak activity in Tropical Cyclone Basins

*After Gray (1975) /Dr. J. Marshall Shepherd (University of Georgia/NASA)*

## Characteristics of TC precipitation

- Stratiform and Convective mechanisms
- Stratiform rain ~50% of total rain from TC.

*Frank Marks (HRD)*

*Hurricane Irene (15 October 1999)*

*WSR-88D DPA daily accumulations*

## Slide 5

## TC rainfall peaks when global rainfall is low

Asymmetric-generally more rain in the Northern Hemisphere

Global rainfall is decreasing with increasing latitude while TC rainfall is increasing

TC contributes 10-17% of global rain 15-30° poleward from Equator (subtropics)

**TC rainfall peaks when global rainfall is low**
**Asymmetric-generally more rain in the Northern Hemisphere**
**Global rainfall is decreasing with increasing latitude while TC rainfall is increasing**
**TC contributes 10-17% of global rain 15-30° poleward from Equator (subtropics)**

- TC Rain

*Frank Marks (HRD)*

## Biggest Rain Producers by Country

- Belize		829.8 mm	32.67”		Keith (2000)
- Bermuda	186.7 mm	7.35”		October 1939 Hurricane
- Canada		302.0 mm	11.89”		Harvey (1999)
- Cayman Islands	762 mm		30”		Sanibel Island Hurricane (1944)
**Cuba****	****	****2550 mm****	****100.39”****	****	****Flora (1963)**
- Dominica	422.3 mm	16.63”		Jeanne (2004)
- Dominican Rep.	507.8 mm	19.99”		Cleo (1964)
- Guadeloupe	508 mm		20.0”		Marilyn (1995)
- Haiti		1447.8 mm	57”		Flora (1963)
- Honduras	912 mm		35.89”		Mitch (1998)
- Jamaica		2451 mm	96.50”		November 1909 Hurricane
- Martinique	450.1 mm	17.72”		Iris (1995)
- Mexico		1634.0 mm	64.33”		Wilma (2005)
- Nicaragua	1597 mm	62.87”		Mitch (1998)
- Panama		695 mm		27.36”		Mitch (1998)
- Puerto Rico	946 mm		33.29”		Eloise (1975)
- St. Maarten	866.6 mm	34.12”		Lenny (1999)
- United States	1219 mm	48.00”		Amelia (1978)
- Venezuela	339 mm		13.35”		Bret (1993)

## United StatesUnits in cm

**2005 US Summer rain**

**2005 US TC rain**

*Frank Marks (HRD)*

## Tropical Cyclone vs. Total Seasonal Rainfall in Mexico

*Art Douglas (Creighton University)*

## United States

## 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

## Percent of Wettest Southwestern TC Rainfall Per Time Frame (hours)1992-2006 (8 cases)

**Average   .56   .94   1.10  1.26  1.70  2.00  2.83  3.15   4.64  5.02  5.05**
**Max.        .90  1.60  2.20  2.60  3.10  3.20  4.00  6.60 10.24 12.01 12.01**

## Mexico

## Tropical Cyclone QPF

## Factors impacting rainfall distributions in landfalling TC’s

- Time of day – core rainfall overnight/ outer band rainfall during day
- Storm size (positive) – the bigger the storm, the more it rains at any given spot
- Topography – Positive in the upslope areas, but negative past the spine of the mountains
- Wind shear (negative) – leads to a quicker dropoff in rainfall for inland TCs
- Nearby synoptic-scale features/Extratropical Transition

**Factors impacting rainfall distributions in landfalling TC’s**

## TC Model Track Error (km) (2002-2006)

## Time of Day – Alberto, July 4-5, 1994

- 04/18z

- 00z

- 05/06z

- 12z

- 18z

## Storm Size

| <2 degrees | “Very small/ midget” | Charley |
| --- | --- | --- |
| 2-3 degrees | “Small” | Allison |
| 3-6 degrees | “Average” | Frances |
| 6-8 degrees | “Large” | Wilma |
| >8 degrees | “Very large” | Gilbert |

- Determined by distance from center to outermost closed isobar

*Joint Typhoon Warning Center*

## How Mountains Affect the Precipitation Distribution

- http://www.prism.oregonstate.edu/index.phtml

**Notes:**
HPC uses the PRISM climatology as a guide for forecasting rainfall maxima in mountain areas.  PRISM data is available for every month of the year for the continental United States.

## Size and Topography

- Hurricane Frances (2004)

## Size and Topography

- Hurricane Juliette (2001)

## Vertical Wind Shear

**Heaviest rain tends to fall left and downwind of the shear vector.**** **
**If the shear is strong enough, all rainfall may move away from the center (exposed center)**

## Depth of Upper Trough Causing Recurvature Key

- Storms which drop most of the rain right of track are steered predominantly by shear lines or through a break in the subtropical ridge. Rainfall tends to be concentrated near and right of track.
- Storms which drop most of their rain left of track recurve due to significant upper troughs in the Westerlies.  Rainfall streaks out well to the north of the system due to jet streaks moving around the upper trough and frontogenesis at the trough’s leading edge.

## Bertha

*Norman W. “Wes” Junker*

## Floyd

*Norman W. “Wes” Junker*

## Bertha (1996) vs. Floyd (1999)

## PRE STATISTICS

**Bosart and Carr (1978) conceptual model of antecedent rainfall**

_**PRE STATISTICS**_

_**Separation Distance**_
**1086 ****±**** 482 km                        Median: 935 km**
_**Event Duration**_
**14 ****± ****7 h                                   Median: 12 h**
_**Time Lag**_
**45 ****±**** 29 h                         Median: 36 h**

## PRE TRACK-RELATIVE POSITIONS

_**PRE TRACK-RELATIVE POSITIONS**_

**26**

**12**

**9**

- Potential for flooding in areas not directly impacted by TC rainfall

## PRE TRACK-RELATIVE POSITIONS

_**PRE TRACK-RELATIVE POSITIONS**_

**26**

**12**

**9**

- Potential for excessive flooding beginning before arrival of TC rainfall

## PRE TRACK-RELATIVE POSITIONS

| Type of PRE
(Number in category) | 24-h rainfall rate statistics (mm) |  |  | Mean PRE speed
(m s−1) |
| --- | --- | --- | --- | --- |
|  | Mean | Std. deviation  | Maximum  |  |
| Left of Track (22) | 185 | 70 | 340 | 10.7 |
| Along Track (8) | 245 | 100 | 410 | 12.9 |
| Right of Track (7) | 260 | 80 | 410 | 5.7 |

**GREATEST RAINFALL**

**SLOWEST MOVEMENT**

## PRE TRACK-RELATIVE POSITIONS

| Type of PRE
(Number in category) | 24-h rainfall rate statistics (mm) |  |  | Mean PRE speed
(m s−1) |
| --- | --- | --- | --- | --- |
|  | Mean | Std. deviation  | Maximum  |  |
| Left of Track (22) | 185 | 70 | 340 | 10.7 |
| Along Track (8) | 245 | 100 | 410 | 12.9 |
| Right of Track (7) | 260 | 80 | 410 | 5.7 |

**HIGH RAINFALL**

**PREs MOVE TWICE AS FAST**

## Along Track PREs

** ****NW/SE oriented trough well to the northeast**
** ****Closed midlevel low NW and flat ridge east of TC**

** ****Broad upper-level jet to the north**
** ****On western edge of θ****e**** ridge**

_**Ernesto (2006)**_

**2100 UTC 060830 700 hPa Ht (dam)                                           and WSI NOWRAD image**

**2100 UTC 060830 925 hPa Ht (dam), ****θ****e ****(K),                             **** and 200 hPa wind speed (m s****-1****)**

## Right Of Track PREs

** ****Large midlevel low NNE and ridge SE of TC**
** ****PREs a bit downstream of where model predicts**

** ****Jet dynamics only partially explain the PREs****	**
** ****No prominent low-level θ****e**** ridge or gradient near PRE**

_**Katrina (2005)**_

**0900 UTC 050830 700 hPa Ht (dam)                                           and WSI NOWRAD image**

**0900 UTC 050830 925 hPa Ht (dam), ****θ****e ****(K),                             **** and 200 hPa wind speed (m s****-1****)**

## Null Case

_**Null Case**_

** ****WNW flow at midlevels**
** ****Scattered rainfall over New England not related to Cindy **

** ****Massive low-level ridge poleward of TC**
** ****No rainfall near low-level ****θ****e**** ridge**

_**Cindy (2005)**_

**0000 UTC 050707 700 hPa Ht (dam)                                           and WSI NOWRAD image**

**0000 UTC 050707 925 hPa Ht (dam), ****θ****e ****(K),                             **** and 200 hPa wind speed (m s****-1****)**

## Rainfall forecasts from landfalling TC’s

- _standard forecasting tools_

**Rainfall forecasts from landfalling TC’s**

-  Empirical Methods
-  In-house Tropical Cyclone Rainfall Climatology
- http://www.hpc.ncep.noaa.gov/tropical/rain/tcrainfall.html
-  GFS/NAM/GFDL/WRF 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

## Rules of Thumb

- Kraft Rule – 1950’s guideline based on a broad grid of first order sites.  Will not indicate the maximum in most cases   (R=100/forward motion in knots).  Environment Canada/Canadian Hurricane Center use a modified version of Kraft which halves this amount since most systems entering the country are sheared.
- 16-inch rule – Long term average of tropical cyclone rainfall maxima which strike the United States.  Vertical wind shear, small sized tropical cyclones, or movement over cooler water prior to landfall can individually lead to a reduction of about half of this figure.  Slow moving and larger than average tropical cyclones lead to higher values than the average.

## TPC Method

**Average Climatological Rain Rate = 2 mm / hour**
**Or about 0.08 in./hour**
**Core Rain Rate = 5 times this Average**
** ****or**
**Core Rain Rate = 10 mm /hour**
**Or about 0.40 in./hour**

*Reinforced by radial amounts computed within Jiang, Halverson, Simpson AMS Hurricane Conference preprint (2006)*

## FREDERIC 

**Storm Name: ___________________****	****Date: ________________ 19__**
**Image Date/Time      Diameter of Storm in ****	****	**
**                                   ****Direction of Motion **
**____________ UTC     _________ deg * 110 km/deg = _________ km**
**____________ UTC     _________ deg * 110 km/deg = _________ km**
**____________ UTC     _________ deg * 110 km/deg = _________ km**
**____________ UTC     _________ deg * 110 km/deg = _________ km**
**Mean Diameter:       D =****	****________ km**

**FREDERIC **

**12 SEPT**

**79**

**12 / 0630**

**12 / 1200**

**12 / 1800**

**12 / 0000**

**5.5**

**5.5**

**4.0**

**4.5**

**605**

**605**

**440**

**495**

**540**

## TROPICAL CYCLONE RAINFALL ESTIMATION

**TROPICAL CYCLONE RAINFALL ESTIMATION**
**HURRICANE FREDERIC, SEPTEMBER 1979**
**6-HOUR CONTINUITY, INFRARED**

## 24

**Forecast translation speed:      V =  _____ deg * 110 km/deg / 18 hrs =  _____ km/hr**
**Mean rainfall rate:      R =  0.2 cm/hr**
**                                        ****D * R  **
**Rainfall Potential:   P = -------**
**                                            ****V**
**                                                               ****km * 0.2 cm/hr**
**                                 ****P = ------------------------------------ = ________ cm**
**                                                                            ****km/hr**
**      **
**Core Rainfall:           C = 5 * P  = ________ cm**
** **
**                **
**                                             ****450                      450**
**Rule of Thumb:        T = ---------------- = ----------------- = ________ cm**
**                                          ****V km/hr                        km/hr**

**24**

**540**

**24**

**24**

**4.5**

**22.5**

**18.8**

**(8.9”)**

**(7.4”)**

**4.0**

## Frederic Rainfall

##  3 event-driven products

-  3 event-driven products
**Eastern Caribbean (40****°W to 67****°W)**
- 	TCCA21 KNHC
- 	MIASTDECA
**Central Caribbean (67°W to 80°W)**
- 	TCCA22 KNHC
- 	MIASTDCCA
**Western Caribbean/Mexico (80°W to 120°W)**
- 	TCCA23 KNHC
- 	MIASTDWCA

## Derived Equation used to Determine TC Rainfall Maxima

**Riehl (1954)**
**Within 30 nm of center –     33.98” per day**
**Within 60 nm of center –       6.30” per day**
**Within 120 miles of center –  0.59” per day**
**Assumes a symmetric/non-sheared hurricane with a gale radius around two degrees of latitude/120 nm.  Does not take into account topography or nearby frontal zones.**

- Rainfall maximum=2*(radial velocity)*(specific humidity in subcloud layer)*(pressure difference within lower km of atmosphere)*(1/radius from center)*(1/g)

## Picking an analog for a TC event

- Size is important...look at the current rain shield and compare it to storm totals/storms 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 nearby fronts/depth of nearby upper troughs for current and possible analogs
- Not all TC events will have a useful analog

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

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

## CLIQR

- Scripts utilize extended best track database from NHC, modified by additional information from HPC/NHC map series and NHC Atlantic non-developing system database
- Storm matches made primarily upon current position, forward motion, and storm size.  In 2009, NHC five day track will be included
- Uses a 9 point system.  The system’s point total can be seen in the last column of text output
- Output generated using CHGHUR/objective guidance messages from NHC, but can also be utilized using manual input
- Simplified output online for active systems at:  http://www.hpc.ncep.noaa.gov/tropical/rain/web/cliqr.html

## CLIQR GUI using manual input

**Notes:**
If there is a current system, the CHGHUR identifier shows up within the Select Storm window.

## CLIQR output via magenta “View Rainfall Graphics” button 

**Notes:**
The .gif comes from my account on the local network.  More Info button calls up the appropriate web page from the Tropical Cyclone Rainfall Project, also from within the HPC network.

## CLIQR web output for active systems

- http://www.hpc.ncep.noaa.gov/tropical/rain/web/cliqr.html

## CLIQR matching storm list (Rainfall Matches hyperlink)

- Simplified list links to relevant storm total rainfall graphic through hyperlink.  Future revisions include columns separating the Puerto Rico impacts from North American impacts to help web user.

## 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)

## 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

## Specialized Tropical Cyclone QPF Guidance

## R-CLIPER

- R-CLIPER (Rainfall Climatology Parametric Model)
- Statistical model developed from TMI data and rain gauges
- Simple model creates a rainfall swath dependent on storm
-   track, intensity, and size
- Operational at 0.25o X 0.25o hourly resolution
- Asymmetries are not taken into account

## R-CLIPER Improvements

** ****Includes shear and topographic effects in 2007**

## TRaP

-  **Can be found at NOAA/NESDIS Satellite Analysis Branch (SAB)**_[http://](http://www.ssd.noaa.gov/PS/TROP/trap.html)__[www.ssd.noaa.gov/PS/TROP/trap.html](http://www.ssd.noaa.gov/PS/TROP/trap.html)_
**Uses microwave rain rate images from SSM/I, TRMM, and AMSU and extrapolates along TC forecast track. METOP and SSMI/S, part of AMSU, expected by the end of the year**
**Only available when a microwave pass “catches” the storm mostly within the swath**
**Depends on official forecast of TC track from NHC, CPHC, etc.**

## TRaP: http://www.ssd.noaa.gov/PS/TROP/trap.html

- TRaP: _[http://www.ssd.noaa.gov/PS/TROP/trap.html](http://www.ssd.noaa.gov/PS/TROP/trap.html)_

## Katrina Rainfall

## Flow of rainfall-related data to and from the Hydrometeorological Prediction Center (HPC)

## Flow of rainfall data to HPC

## Flow of tropical cyclone rainfall forecasts within the National Weather Service (NWS)

**Graphics**
**Four times**
**A day**

**Statement**
**Four times **
**a day**

## Model Forecast Biases/Verification relating to Tropical Cyclone QPF

## QPF Equitable Threat Score

**QPF Equitable Threat Score**

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

- Equitable Threat Score

**Pattern comparisons for U.S. landfalling storms****From 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.)

## HPC tropical cyclone QPF verification since 2004

## Slide 70

## Slide 71

## Slide 72

## Slide 73

## Slide 74

## Slide 75

## Day 1 Threat Scores and Bias

## Day 2 Threat Score/Bias

## Day 3 Threat Score/Bias

## Summary

- Tropical cyclones lead to 10-20% of annual rainfall in South and Eastern U.S. While tropical cyclones lead to a smaller percent of annual rainfall for the Desert Southwest regionally on an annual basis, individual events can lead to a significant portion of the annual rainfall on a local basis.
- Tropical cyclone QPF pattern depends on storm size, forecast track, vertical wind shear, topography, depth of upper trough causing recurvature, and SST field the cyclone moves over prior to landfall
- While climatology is important to keep in mind, TC QPF is heavily based on the guidance which has the best verification and is closest to expected TC track (usually GFS).  NAM and ECMWF both show low biases for higher rainfall amounts.