1. José J. Hernández Ayala Department of Geography University of Florida
Contribution of Tropical Cyclones to the Rainfall Climatology of Puerto Rico
José J. Hernández Ayala
Department of Geography
University of Florida

2. Introduction Important Questions
What is the spatio-temporal distribution of rainfall contributed by TCs?
How Teleconnections such as ENSO and the NAO affect this contribution?
How would a changing climate affect the contribution of rainfall from TCs?
(Knight and Davis 2007; Knight and Davis 2009; Sheperd et al., 2007)
Rainfall arising from tropical cyclones (TC) can be an important water source for agriculture and other applications over subtropical and tropical regions (Rodgers et al., 2001).

3. Study Area -Area: 9,104 km.sq -Population: 3.7 million (Census 2010)
-Pop Density: 418/km.sq

4. The Climate of Puerto Rico

5. Köppen Climate Zones

6. Tropical Cyclones and Puerto Rico
Puerto Rico is subject to frequent and severe impacts from Hurricanes (Dunn and Miller 1964, Simpson & Riehl 1981, Diaz & Pulwarty 1997).
The frequency with which a tropical cyclone passes directly over Puerto Rico is small (Scatena and Larsen, 1991).
A comprehensive study of hurricanes in P.R based on meteorological principles and the historical record is lacking (Boose, Serrano &Foster 2004).
Storm rainfall totals of 500 mm are common for hurricanes in Puerto Rico (Riehl, 1979).

7. Previous Studies I

8. Previous Studies II

9. Problem Statement
Understand the contribution of TCs to the rainfall climatology of the island.
Do TCs have different contributions to the rainfall climatology of the island in different regions?
Do some hurricane season month’s exhibit higher or lower rainfall contributions from storms?

10. Hypotheses
Rainfall associated from TCs is highly concentrated in the eastern portion of the island where El Yunque National rain forest is located.
A general decrease in storm precipitation is observed as you move from the eastern to the western region of the island.
TCs will tend to contribute more to the rainfall climatology of stations in the eastern and southern regions of the island especially during the peak hurricane season months of August, September and October.
The south will also have high rainfall contribution percentages since this region is the driest of the island, and for that reason any precipitation generating process that impacts the area has an important contribution to its rainfall climatology.

11. Data
Six-hourly TC positions were obtained from the International Best Track Archive for Climate Stewardship (IBTrACS) (Knapp et al., 2010) for the years 1970 through 2010.
Daily and monthly rainfall totals were obtained from the National Climatic Data Center (NCDC), for 32 weather stations located on the main island of Puerto Rico for the period of

12. Rain Gauge Stations and Elevation

13. TC Tracks
86 TCs were identified as the ones that passed within a 500 km around the island.
Most move east to west, only a few events move west to east.

14. Methods
The contribution of rainfall associated with TCs will be estimated for each month of the hurricane season (June-November) by calculating a percentage between monthly total and daily rainfall for all 86 TCs over the period.
After the percentage for each hurricane season month is calculated for all weather stations the next step will be to map the percentages for each month.
Natural Neighbor and Ordinary kriging interpolated surfaces for all hurricane season months were generated to identify spatial patterns of high/low contribution percentages.

15. Results Hurricane Season Months (J-N)
NN Season
OK Season

16. Results June and July
NN June
OK June
NN July
OK July

17. Results August and September
August NN
August OK
September NN
September OK

18. Results October-November
OK October
NN October
NN November
OK November

19. Conclusions
TCs contribute as much as 15% of the rainfall during the entire Hurricane season in some portions of the south.
June has the lowest contribution while July shows that storms contribute as much as 11% in the central south.
August and September have the highest contributions of rainfall associated with TCs, with some areas in the east and south exhibiting percentages of 26% and 34%.
October shows TC rainfall contributions of 12-15% in the east and south while November exhibits lower contributions of 5-7% in the southeast.
All Hurricane season months show a decreasing trend in contribution from east to west.

20. Limitations
Limited by the use of only 32 stations with data for the period.
There are some areas of the island that are not well represented.
Not having sufficient observations in the central mountains is a huge limitation since topography plays a big role when it comes to understanding rainfall patterns in the island.

21. Future Work
Understand TC rainfall contribution variability, connections with ENSO, AMO, NAO?
Understand changes in TC rainfall contribution and its connections with climate change?

22. Questions?