Month: September 2017

Thoughts on strengthening

The following bothers me:

The pressure dropped 10 millibars, but the wind speed was held constant at 160 kts (184 m/h).  The decrease in pressure normally indicates an increase in wind speed potential.  However, the scientist think the storm is going through an eye wall replacement cycle, which will stop the wind speed from increasing.

Note: This storm is huge. If it makes it into the Gulf of Mexico, coastal Louisiana will feel the affects of it regardless of where it will make landfall.  The question is only one of severity.  The storm is still a long way off, but it is chugging alone.

ADV LAT LON TIME WIND PR STAT
27 17.10 -59.80 09/05/18Z 160 926 HURRICANE-5
28 17.40 -61.10 09/06/00Z 160 916 HURRICANE-5

 

BULLETIN
Hurricane Irma Intermediate Advisory Number 28A
NWS National Hurricane Center Miami FL AL112017
200 AM AST Wed Sep 06 2017

...EYE OF POTENTIALLY CATASTROPHIC CATEGORY 5 HURRICANE IRMA
PASSING OVER BARBUDA...


SUMMARY OF 200 AM AST...0600 UTC...INFORMATION
----------------------------------------------
LOCATION...17.7N 61.8W
ABOUT 5 MI...10 KM N OF BARBUDA
ABOUT 40 MI...65 KM N OF ANTIGUA
MAXIMUM SUSTAINED WINDS...185 MPH...295 KM/H
PRESENT MOVEMENT...WNW OR 285 DEGREES AT 15 MPH...24 KM/H
MINIMUM CENTRAL PRESSURE...914 MB...26.99 INCHES

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Why the uncertainty in the turn?

Ok, it's very simple:  The turn is 5 days out.  Mathematically speaking, you can't accurately forecast 5 days out.  But, there is a small bit of information missing:  The steering current that is supposed to cause the turn is characterized as a "small wave." The question plaguing me is will this "small wave" be strong enough to allow a Cat 4 or 5 storm rotate on its axis?  It's 5 days out.  You can't know.

So, here's the deal:  The storm, as all storms do, wants to turn north, but there is a bulk of air that is forcing it to head west.  This bulk of air isn't supposed to let up until the 5th day allowing Irma to turn.  However.... 5 days is a long time in weather forecasting.

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2017 Sep 4 - Irma Yuck - Jogged SW

Weather Underground models

OK.  This does concern me.  But, I stand firm, that it is still too early to work ourselves up.  However, while you are eating your hamburgers and hot dogs, it might not be too bad of a deal if you struck up a conversation about where you want to spend a few days in a couple of weeks.... maybe.

Irma is still more than 5 days out.  Projects loose accuracy quickly after the 3rd day.

Of note, in the discussion, NOAA is projecting that the storm will not only maintain, but increase its strength.  If there forecast of strengthening is wrong, then at best it will maintain.  Neither is good and I will be watching, with fervor, for a forecast change.

2017 Irma 5-day Projection
5-day projection from NOAA

What follows is the forecast discussion copied from NOAA's website. Keep in mind that NOAA is the sole generator of data for Atlantic storms. Everyone else, takes NOAA's data and interprets it. This includes the newscasters, me, your local government entities and NWS. Tropical data is NOAA's responsibility. Getting it to the public is everyone else's.

000
WTNT41 KNHC 040854
TCDAT1


Hurricane Irma Discussion Number 20
NWS National Hurricane Center Miami FL AL112017
500 AM AST Mon Sep 04 2017


Irma's signature in infrared satellite images has been improving
over the past few hours. An eye has appeared and is warming, and
the central dense overcast has become more symmetric. Although the
satellite presentation is better than when a NOAA plane
investigated Irma last evening, the initial intensity will be held
at 100 kt for now. Another NOAA P3 aircraft is just now beginning
to sample the hurricane and should provide an updated intensity
estimate during the next few hours.


A strong, stationary mid-tropospheric high centered over the central
Atlantic is forcing Irma on a west-southwestward course, and the
initial motion estimate remains 255/12 kt. Irma will begin
rounding the southwestern edge of the high soon, which will allow
the hurricane to turn westward later today and then west-
northwestward in 36-48 hours. Down the road, a large mid-latitude
trough is expected to dig southward over the eastern United States
during the next 72 hours, but the global models have been trending
toward quickly lifting the trough out over New England and eastern
Canada on days 4 and 5, with the subtropical ridge building westward
toward Florida. As a result, it's becoming increasingly likely that
Irma would maintain a west-northwestward heading on days 3 through
5, and the track guidance shifted significantly westward on this
cycle during that period. Remarkably, the track models are very
tightly clustered through day 5, which increases the confidence in
the westward shift of the latest NHC forecast.


All environmental factors suggest that Irma will at least maintain
its intensity for the entire 5-day forecast period, if not
strengthen gradually. Oceanic heat content values increase along
Irma's forecast path, mid-level moisture will be more abundant, and
vertical shear appears to be generally low. As a result, the NHC
intensity forecast continues to call for gradual intensification
through at least 72 hours, with a possibility for some slight
weakening by days 4 and 5 (but still as a major hurricane). As with
any major hurricane, Irma's intensity may fluctuate around these
forecast intensities, but the overall trend is for a gradual
increase of the maximum winds, assuming Irma's core does not move
over any of the islands in the Greater Antilles.


Users are reminded to not focus on the exact forecast track since
strong winds and heavy rainfall extend well away from the center.
In addition, average NHC track errors are about 175 and 225 statute
miles at days 4 and 5, respectively.


KEY MESSAGES:
1. Irma is expected to affect the northeastern Leeward Islands
within a couple of days as a major hurricane, accompanied by
dangerous wind, storm surge, and rainfall impacts, along with rough
surf and rip currents. Hurricane watches are in effect for
portions of the Leeward Islands, and additional hurricane or
tropical storm watches or warnings will likely be issued later
today. Residents in these areas should monitor the progress of Irma
and listen to advice given by officials.


2. Irma is expected to remain a dangerous major hurricane through
the upcoming week and could directly affect the British and U.S.
Virgin Islands, Puerto Rico, Hispaniola, the Turks and Caicos, the
Bahamas, and Cuba. Residents in all of these areas should monitor
the progress of Irma and listen to advice given by officials.
Tropical storm or hurricane watches will likely be issued for the
British and U.S. Virgin Islands and Puerto Rico later today.
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