Tropical weather analysis - September 6, 2013

By: KoritheMan , 6:07 AM GMT on September 06, 2013

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Lorena

Tropical Storm Lorena continues to approach southern Baja California. As of the just released NHC intermediate advisory, the following information was posted on the cyclone:

Wind: 40 mph, with higher gusts
Location: 21.0°N 107.8°W
Movement: NW at 13 mph
Pressure: 1005 mb

The 6z satellite estimate should be up soon, but are unavailable as of this writing; the 0z estimates supported a 35 kt tropical storm. Satellite images show a cloud pattern that is a little better organized, with evidence of banding features wrapping into the southern quadrant of the circulation. The low-level center is a little difficult to locate, but based on radar data, microwave, and satellite fixes, I assume that it is on the southwestern side of the convective cloud tops.



Figure 1. Latest infrared satellite image of Tropical Storm Lorena. Image credit: NOAA's Satellite Services Division (SSD).

Lorena is over SSTs of 29-30C, and the near-storm vertical shear appears weak. The cyclone could thus intensify a little prior to making landfall across southern Baja in about 24 hours. The overall guidance envelope has shifted eastward between 18z and 0z, with a track now more clustered over the southern peninsula. My forecast follows this reasoning, showing a landfall in southern Baja in about 24 hours, followed by a gradual northward turn as Lorena rounds the western periphery of a deep-layer ridge anchored over the southwestern United States. The global model fields suggest that the low-level remnants of Lorena will shear off from the mid-level center, with the former heading west back into the open Pacific, while the latter streams northward ahead of a deep-layer trough off the west coast of the United States. My forecast track shows a considerable slowing of the forward speed in response to this likelihood. It is also possible that Lorena could dissipate sooner than forecast.

The primary threat in connection with Lorena is heavy rainfall; waters off this section of Baja are rather warm, and the deep convection seen on satellite imagery reflects that. These rains are likely to cause flash flooding and mudslides, and people in the region should carefully follow the progress of Lorena. The heavy rain threat may stream northward into the southwestern United States in a few days once the cyclone shears off. Winds to tropical storm force, especially in the mountains, are also possible.

Intensity forecast and positions

INITIAL 09/06 0300Z 20.4°N 107.6°W 35 KT 40 MPH
12 hour 09/06 1200Z 21.8°N 108.8°W 40 KT 45 MPH
24 hour 09/07 0000Z 23.3°N 109.8°W 40 KT 45 MPH...INLAND
36 hour 09/07 1200Z 24.1°N 110.6°W 30 KT 35 MPH...INLAND
48 hour 09/08 0000Z 24.7°N 111.1°W 25 KT 30 MPH...INLAND
72 hour 09/09 0000Z 24.9°N 111.1°W 20 KT 25 MPH...POST-TROPICAL/REMNANT LOW
96 hour 09/10 0000Z...DISSIPATED

Track forecast



Figure 2. My forecast track for Lorena.

NHC storm information

000
WTPZ32 KNHC 060546
TCPEP2

BULLETIN
TROPICAL STORM LORENA INTERMEDIATE ADVISORY NUMBER 4A
NWS NATIONAL HURRICANE CENTER MIAMI FL EP122013
1100 PM PDT THU SEP 05 2013

...LORENA CONTINUES AS A TROPICAL STORM PARALLELING THE MEXICAN
COAST...


SUMMARY OF 1100 PM PDT...0600 UTC...INFORMATION
-----------------------------------------------
LOCATION...21.0N 107.8W
ABOUT 145 MI...235 KM WNW OF CABO CORRIENTES MEXICO
ABOUT 190 MI...305 KM SE OF CABO SAN LUCAS MEXICO
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...NW OR 325 DEGREES AT 13 MPH...20 KM/H
MINIMUM CENTRAL PRESSURE...1005 MB...29.68 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* BAJA CALIFORNIA SUR FROM AGUA BLANCA TO BUENAVISTA

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* BAJA CALIFORNIA SUR NORTH OF AGUA BLANCA TO SANTA FE

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA...IN THIS CASE WITHIN THE
NEXT 24 TO 36 HOURS.

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...IN THIS CASE WITHIN THE NEXT 36 TO
48 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1100 PM PDT...0600 UTC...THE CENTER OF TROPICAL STORM LORENA WAS
LOCATED NEAR LATITUDE 21.0 NORTH...LONGITUDE 107.8 WEST. LORENA IS
MOVING TOWARD THE NORTHWEST NEAR 13 MPH...20 KM/H...AND THIS MOTION
IS EXPECTED TO CONTINUE THROUGH FRIDAY MORNING. A SLOWER
NORTHWESTWARD MOTION IS EXPECTED TO BEGIN LATE FRIDAY...FOLLOWED BY
A TURN TOWARD THE NORTH-NORTHWEST BY LATE SATURDAY. ON THE FORECAST
TRACK...THE CENTER OF LORENA WILL APPROACH THE SOUTHERN BAJA
CALIFORNIA PENINSULA ON FRIDAY AND THEN BE NEAR OR OVER LAND BY
SATURDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 40 MPH...65 KM/H...WITH HIGHER
GUSTS. SOME STRENGTHENING IS POSSIBLE DURING THE NEXT 24 HOURS OR
SO. WEAKENING IS FORECAST TO BEGIN BY FRIDAY NIGHT OR SATURDAY
WHEN LORENA BEGINS TO INTERACT WITH LAND.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 80 MILES...130 KM
NORTHEAST OF THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1005 MB...29.68 INCHES.


HAZARDS AFFECTING LAND
----------------------
RAINFALL...LORENA IS EXPECTED TO PRODUCE TOTAL RAINFALL
ACCUMULATIONS OF 3 TO 5 INCHES OVER THE SOUTHWEST COAST OF MEXICO
AND THE SOUTHERN PORTION OF THE BAJA CALIFORNIA PENINSULA...WITH
ISOLATED MAXIMUM AMOUNTS OF 10 INCHES POSSIBLE. THESE RAINS COULD
PRODUCE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES.

WIND...TROPICAL STORM FORCE WINDS ARE EXPECTED TO BEGIN IN THE
WARNING AREA FRIDAY AFTERNOON AND COULD CONTINUE THROUGH SATURDAY.
TROPICAL STORM FORCE WINDS ARE POSSIBLE IN THE WATCH AREA SATURDAY.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...200 AM PDT.

$$
FORECASTER LANDSEA/AVILA



Invest 99L

An area of low pressure is producing a large area of cloudiness and thunderstorms over the southern Bay of Campeche. Satellite, surface, and earlier reconnaissance data suggest that the system lacks a well-defined center of circulation. However, a tropical depression or tropical storm could still form before the system moves inland over eastern Mexico later today.

Regardless of development, very heavy rain and flash flooding will impact the state of Veracruz over the next couple of days.

Probability of development in 48 hours: 50%

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.