1. José J. Hernández Ayala
Department of Geography
University of Florida
Contribution of Tropical Cyclones to
the Rainfall Climatology of
Puerto Rico
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).
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).
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 1970-2010.
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
1970-2010 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
0.07
5.26
16.61
19.50
7.90
2.80
8.69
0.00
5.00
10.00
15.00
20.00
25.00
June July August September October November Season
MeanPercentage(%)
Hurricane Season Monts
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 1970-2010
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?
