In response to a question about where (in Bahamas/Caribbean) to spend Hurricane Season:

It might help to break your thought process into 2 parts:

1. Avoidance: Lying in places where Tropical LO pressure systems of significant intensity are highly-unusual.

2. Protection: Selecting a relatively-secure spot when you lie in areas at higher risk.

First, AVOIDANCE:

Safest place I can think of in Caribbean/Bahamas area is Panama – I don’t know that a Tropical LO has ever (in recorded history) seriously impacted Panama (I’m not saying one can’t, but it seems unlikely).

From an avoidance perspective, 2nd safest place is probably Colombia, followed by ABCs/Venezuela, and Trinidad/Tobago. All of these areas have some risk for Tropical LO pressure systems – but, because of the normal E-to-W progression of such systems, these areas are prone to being impacted by the LEFT-quadrant of the LO (the WEAK quadrant, but a quadrant with W-component wind)…AND Tropical LOs S of Latitude 12N tend to be relatively-weak.

Second, PROTECTION:

When you’re in a higher-risk area, the more advance warning you have of an impending system, the more options you have to secure your vessel in an optimum location. I can help you with this by providing the maximum advance warning, and offering an educated guess on the plausible tracks a system might take, as well as its plausible intensity.

Unlike most forecasts which focus on 1 single correct solution, I try to appraise you of all “plausible” risks.

Almost any location can be a good spot in a Hurricane – if it’s in the correct place relative to the path of the Hurricane.

That said, there are certainly places which offer very good protection in all but the worst-case scenarios:

The most-secure spot for protection may be Luperon,DR, for at-least 3 reasons:

1. DR N Coast would be in the LEFT-quadrant of a W-moving LO
2. most Hurricanes track W or N-of-W, and thus, before reaching Luperon, would travel over-or-adjacent-to the large landmass of DR E of Luperon (and likely PuertoRico) – weakening the LO before it gets to Luperon
3. in order to be impacted by the RIGHT-quadrant of a Hurricane, it would almost certainly be moving from S-to-N, and would cross the large & mountainous Hispanola landmass before reaching Luperon.

RioDulce, Guatemala is an excellent spot – it’s up a river.

Other than Luperon and the RioDulce, there are MANY good “Hurricane Holes” – but probably none of them offers 100% protection when hit in just-the-wrong-way by a Cat5 Hurricane.

Among the many good Hurricane Holes (and there are LOTS of others in addition to these):

• Several spots in Abacos
• Georgetown,Exuma
• Salinas, PR
• A few select spots in StMartin, Antigua, StLucia, Grenada, among others

*.*

TIMING of Hurricane Season:

Of course, Hurricane Season “officially” runs from June 1 thru November 30.

But Tropical LOs have occurred in the Atlantic N of the Equator in every month except 1 – I believe it’s February. Weather does not obey the calendar, and, if the right (or should I say wrong) conditions come together, a Hurricane is possible anytime.

That said, the most active part of the season varies by geography:

For E Caribbean, probably 95% of Tropical LOs pass from August 1 to October 15 (“Cape Verde Season”, where LOs tend to develop in E Tropical Atlantic). Probably 90% of systems pass in just 6-weeks, from August 15 to September 30. But I can recall Tropical LOs in recent years in every month from April to November – indeed “wrong-way-Lenny” raked the NE Caribbean as a Cat5 in mid-November!

For W Caribbean (and all areas N of the Caribbean), high-risk times are longer…not only is there high risk from LOs moving W from E Caribbean (during the “middle” of season)…but also from LOs which develop along stalled ColdFRONTs, (during the “ends” of season from April-July and October-December).

It’s been a long time coming, but the new, improved, expanded 5th Edition of my weather book will be available for shipping about Friday, Feb 15, 2013.

5th Edition will include greatly expanded sections on:

• local effects, and how to apply them to forecasts
• 500mb/upper-air weather and its effects on surface weather
• GRIB data and GRIB viewing software

The book has been out-of-print since about December 1, 2012.

On about Thursday Feb 14 or Friday Feb 15, I’ll contact everyone who purchased a book since about December 1, 2012, to determine whether you want me to:

• ship book to the address you specified at time of order
• ship book to a different address
• cancel order and refund money

Thank you for your support!…Chris.

Primer for W Caribbean email forecasts

I try to choose my words carefully. I am as specific as I can be. If I speak about something in general terms, or impacting a general area, it means I don’t have sufficient information to make a more-specific guess, and/or it applies throughout the area.

Forecast is in several parts:

1.) Recent observational data.

2.) Analysis of current satellite / RADAR imagery.

3.) Synopsis of weather features, sometimes with a general discussion of predicted conditions in some areas of the region.

4.) Specific forecasts for Precipitation (and squalls) / Winds / Seas. This is normally divided by weather-parameter (Precipitation first, then Wind, then Seas). One reason – if the forecast is wrong, you may see conditions similar to adjacent areas…so it’s useful for
you to be aware of the forecast for adjacent areas. Occasionally, I’ll break this section down by LOCATION, with each parameter (Precip, Wind, Seas) discussed by location.

PRECIP - I usually discuss coverage (in order of increasing coverage: isolated / scattered / numerous or widespread). I also discuss character of precip (convergence can be nasty, but not severe, while convective has potential to be severe), and try to offer a guess as to wind anomalies in the precip – sometimes as wind speed “added to gradient wind”,
sometimes as total wind in squalls.

WIND - speed & direction, as follows: Direction: I usually give this in degrees TRUE. The forecast is NOT so accurate that you should really expect wind of 070-degrees to be from
070-degrees. My main reason for specifying 070-degrees is to offer you insight into the TREND in wind direction. 070-degrees is just about ENE. 060-degrees is ENE. A change from 070 to 060 suggests a BACKING TREND to the wind direction, rather than a forecast for those numbers specifically.

Speed: in kts. I usually only give a specific number, such as 18k. You should mentally “bracket” this – I’m not predicting a steady 18k – you should read this as 18k greater variance…in the case of 18k, you should interpret this as a forecast for 15-21k. If I say “gusty”, add another 20% for gusts, which would make the forecast for 18k & gusty = 15-25k.

Two reasons I give specific wind velocity, rather than brackets: 16k &18k are both “15-20k”. 18k today & 16k tomorrow suggests a TREND of decreasing wind. TRENDS are very important in your decision-making. Also, it saves several characters – many clients receive forecasts on slow email connections, and every character we can shave off we do.

You may notice the < sign occasionally. It describes a trend. For instance 090@12<15 means 090-degree wind building from 12k to 15k during the applicable period.

Sometimes, I give wind direction in “cardinal” units (N or NW or SSE, etc.), or wind speed in brackets – I do this when I’m so uncertain that I can’t get more specific.

REMEMBER TO CONSIDER WIND IN SQUALLS! My “wind” forecast is generally for wind in the absence of significant squalls. ALWAYS refer to the “PRECIP” forecast for wind in squalls!

SEAS - I give height, periodicity, and direction. Sometimes I specify wind-chop versus swell. Sometimes I give both. If I give both, you should neither add the two nor just look at the largest sea. The real answer is inbetween – generally take the larger sea & add half of the smaller sea to get the total height. Each vessel responds to different seas in a different manner. If you know what’s out there, you can make an educated guess about how your vessel will respond.
GEOGRAPHY:
* *
For vessels transiting ColombianCoast…
Very briefly…when Trade winds are in place, semi-permanent LO over Colombia causes large compression zone with strong wind. Though this zone moves, it’s typically 20-120 mi from shore, between 74W-76W (but it often penetrates all the way to the Coast from the SantaMarta area to 11N/76W), and I try to accurately gauge the strongest of these winds as the “wind-maxima” (I predict sustained wind – gusts will be higher). Winds within 20 miles of the Coast between 72W-74W tend to be lighter, and may vary in a day/night diurnal pattern, and are hard for me to gauge.
* *
For vessels transiting from Cartagena to the SanBlas area…
WIND: for conditions on your departure, refer to the “Just SW of Cartagena area” part of the “Colombia” forecast. For conditions toward your arrival, refer to “E Panama”. S of Cartagena winds are often lighter & more variable in direction (see below).
SEAS:
The 1st forecast given for SW Caribbean is a general forecast for seas offshore near 12N/78W…Coastal seas from Cartagena SW-ward may be somewhat-lower. I usually mention seas in “Coastal E Panama”, which probably better represent seas along most of the journey from Cartagena to SanBlas.
Precip:
This is broad-brushed…suggest you use the E Panama forecast, unless there’s detail in the Colombia area.
* *
From Cartagena S&W toward Colombia-Panama border…the forecast can vary considerably with areas toward 8N-9N frequently seeing lighter wind & more-likely with a tendency to be NW-N…and even S-W when this area is near-or-S-of the ITCZ. Conditions vary too-much from location-to-location to make a Regional Email Forecast useful. It’s probably more-useful to be aware of the overall weather pattern in this area, and assume conditions at a given location will change little from day-to-day, unless there’s a change to the overall pattern and/or location of the ITCZ.
* *
E Panama includes the SanBlas & adjacent areas, and W to the turn in the Coast toward Colon near 79-40W. NNE-NE Trades are typically-lighter toward Colon. W Panama includes BocasDelToro & adjacent areas. There is sometimes an ENE-to-WNW wind shift somewhere between Colon & BocasDelToro, but the location of this shift varies.
* *
P-S-A stands for Providencia-SanAndreas-AlbuquerqueCays, and adjacent reefs/islands (generally 12N-14N from 80W-82W).
* *
Honduras forecasts generally focus on the greater BayIslands area between 86W-87W. Conditions can vary greatly E of 85W, but this area is typically transited briefly.
* *
Conditions also vary from about 87W (sometimes including Utila) along Honduras to the RioDulce & S Belize…and I frequently mention this area as the “SW Corner of NW Caribbean”…where usually-lighter (sometimes W-N) wind varies greatly-by-location, making a forecast difficult.
* *
During periods of enhanced E-SE wind & also following a ColdFRONT, a large zone of enhanced wind often develops within 100mi N & E & sometimes NW of the BayIslands – I try to gauge this correctly, but sometimes it’s difficult to anticipate the onset of these enhanced winds which can effect vessels transiting offshore from Belize to the BayIslands, and often Guanaja, sometimes Roatan.
* *
ColdFRONTs typically lack much energy when they move thru NW (and SW) Caribbean, and clocking S-W wind is unusual (it’s more-common Mexico’sYucatan). Severe weather accompanying a FRONT is almost always due to tight gradient & convergence (often with some instability causing the most-severe squalls along FrontalTROF) as HI pressure establishes behind a FRONT – and this can be quite severe, with wind deviating from computer models – exceeding velocity & more W-N in direction (I try to gauge this correctly) – this is possibly due to cooler air funneling E-SE from BayOfCampechee and also S&E down the Yucatan landmass & E thru Honduras (sometimes onward S thru Nicaragua & CostaRica to W Panama), versus the milder Marine airmass. When a strong ColdFRONT passes, with clocking wind for Honduras, Panama and P-S-A should watch-out!
* *
Mexico forecast focuses on the IslaMujeres-Cozumel area, N of 20N. For S of 20N, average the Mexico & Belize forecasts in all respects, unless specified otherwise.
* *
Other areas (Jamaica / Caymans / Cuba / S Coast of Haiti & DomRep / offshore passage routes) are not frequented by Cruising vessels (except briefly in-transit), and are only covered briefly. Contact me for a Custom Forecast for these areas. N of Caribbean use Bahamas/W Atlantic forecast.
* *
If you have any insights to contribute to this brief guide, please send them to me. Hope this helps…Chris.

TYPES of forecasts:
“EarlyBriefing” is sent each morning (90%+ of the time) in order to get you the information you need to make decisions about today.
Normal forecast usually arrives mid-day.
“InterimTropical” is issued for ALL REGIONS when significant Tropical weather is possible.
Other “Interim” emails may be issued for Earthquakes/Tsunamis or significant weather events or emergencies.
“Schedule” emails alert you to changes to Marine Weather Center operations.

Normal Forecasts are in 5 parts:

1.) Recent observational data (ASCAT, sometimes Microwave satellite winds, BUOY observations).

2.) Analysis of current satellite / RADAR imagery.

3.) Synopsis of weather features, sometimes with a general discussion of predicted conditions in some areas of the region. Synopsis is either by-area or day-by-day, depending on how I can best generalize the pattern.

Areas:
SE Caribbean typically Martinique-Trinidad.
NE Caribbean typically Dominica-Leewards-VI-PR (always S Coast of PR unless specified)
DR is always N Coast of DR unless specified
Venezuela is offshore Islands near 11N-12N (LosTestigos-LosRoques) unless specified
ABCs is Aruba-Bonaire-Curacao
NOTE: for locations near the boundary between areas, you should average conditions in the 2 areas. For instance, if you’re transiting waters between StLucia-Guadeloupe, and I only give a forecast for SE Caribbean / NE Caribbean, then you’ll average the 2 forecasts.
When conditions vary within an area, I’ll usually break that area into smaller pieces.

4.) Outlook for 5-10 days, or as far into the future as I can make a guess.

5.) Specific forecasts for Precipitation (and squalls) / Winds / Seas.
This is normally divided by weather-parameter (Precipitation first, then Wind, then Seas). One reason for by=area: if the forecast is wrong, you may see conditions similar to adjacent areas…so it’s useful for you to be aware of the forecast for adjacent areas. Occasionally (during significant weather events), I’ll break this section down by LOCATION, with each parameter (Precip, Wind, Seas) discussed by location.

PRECIP – I usually discuss coverage (in order of increasing coverage:
isolated / scattered / numerous or widespread). I also discuss character of precip (convergence can be nasty but not severe, while convective has potential to be severe), and try to offer a guess as to wind anomalies in the precip – sometimes as wind speed you should add to gradient wind (i.e. “5k enhanced wind”), sometimes as total wind in squalls (i.e. “to 30k”).

WIND – speed & direction, as follows:
Direction: I usually give this in degrees TRUE. The forecast is NOT so accurate that you should really expect wind of 070-degrees to be from 070-degrees. My main reason for specifying 070-degrees is to offer you insight into the TREND in wind direction. 070-degrees is just about ENE. 060-degrees is ENE. A change from 070 to 060 suggests a BACKING TREND to the wind direction, rather than a forecast for those numbers specifically.

You may notice the < sign. You should read “<” as the word “becoming” – it describes a trend. For instance 090@12<15 means 090-degree wind building from 12k to 15k during the applicable period.

Speed: in kts. I usually only give a specific number, such as 18k. You should mentally “bracket” this ± 20%…in the case of 18k, you should interpret this as a forecast for 15-21k. “g” means “gusty”. Forecast 18g23k means 18k sustained, gusting 23k. Of course, you’ll bracket this, so you’ll expect 15-21k sustained, gusting 19-27k.

Two reasons I give specific wind velocity, rather than brackets: 16k & 18k are both “15-20k”. 18k today & 16k tomorrow suggests a TREND of decreasing wind. TRENDS are very important in your decision-making. Also, it saves several characters – many clients receive forecasts on slow email connections, and every character we can shave off we do.

During significant weather events, when I feel it’s more important to convey the overall wind possibilities than to convey coverage of squalls, I’ll sometimes use the letter “s” (for wind in squalls) in the wind forecast. For instance, 30g37s50k means 30k sustained wind, gusting 37k, squalls to 50k.

Sometimes, I give wind direction in “cardinal” units (N or NW or SSE, etc.), or wind speed in brackets – I do this when I’m so uncertain that I can’t get more specific.

REMEMBER TO CONSIDER WIND IN SQUALLS! My “wind” forecast is generally for wind in the absence of significant squalls. ALWAYS refer to the “PRECIP” forecast for wind in squalls!

SEAS:
Seas are a bit messy to interpret. Forecast for seas assumes you’re in deep water, and in an area completely exposed to the Ocean. Seas within the Islands of the Virgins will be lower – the extent to which they’re lower depends on your location. Seas (and wind) between Islands in the Windward/Leewards are typically higher than over open waters (away from Islands)…and the Islands also bend wind & sea directions locally.

Again, my forecasts for wind & seas assumes you’re in exposed areas, and away from the local effects imparted by Islands…

What you really care about is the ACCELERATION of motion of your vessel due to seas. By acceleration, I mean any change in motion versus what you’d have with flat calm seas.

6′ seas with a 7-sec interval from the E will have a different impact on your vessel (seas will cause different acceleration) on a 30′ sailboat versus a 50′ sailboat…and different for any given boat if you’re heading in a different direction, etc., etc.

But, IN GENERAL, seas with an interval much greater than 1-second-per-foot of height are swells. And swells are less-bad than wind-driven chop.

For instance, 6′ seas with 6-sec interval is a wind-chop. 6′ seas with 8-sec interval is a short-interval swells. 6′ seas with a 12-sec interval are long-interval swells. Swells are less-steep, and, therefore, impart less acceleration on the vessel for a given height.

As for adding height…unless different wave trains PHASE, there’s no need to add height. However, individual waves from each wave train DO PHASE. Think of it this way:

If you encounter the crest of an individual 6′ NE swell at the same as you encounter the crest of an individual 6′ E wind-driven wave, then the total height of the perfectly-phased wave will be close to 8-10′ (about 50% larger).

Why?
Let’s say you have a 6′ wind-chop and no swell. The 6′ wind-chop causes height of the ocean on which your vessel is floating at one instant in time to be 3′ higher or 3′ lower than the mean sea-level.

But if the crest of the 6′ wind-chop occurs where the height of the sea is 3′ above mean sea-level (because you’re at the top of a swell)…then, at the top of the phased swell-and-chop, you’re 6′ above mean sea-level.

Since the wind-chop and swell are of different intervals, they are not likely to remain in-phase at the trough of that wave, so you’re not likely to be lower than about 3-4′ below mean sea-level at the trough…for a total height of 9-10′ from crest-to-trough in the above example.

So, as a rule, when there is a swell and a wind-chop, I would add up-to-50% of wind-chop height to the swell to arrive at the total height of seas.

NOT all seas you encounter will be this high…
When there’s only 1 wave-train, as many as 1-in-200 waves can be 50% higher than the significant sea height.
When there’s a combination of wind-chop and swell, and especially when they’re from different directions, SOME waves will phase (at-least partially) and cause many many more waves to be 50%+/- higher than the swell height.

Here’s how I’d use my sea-state forecast in decision making:

Assess whether each wave train, by itself, is acceptable.

If so, then assess whether adding 50% of wind-chop height to the swell would be acceptable.

If so, then assess whether wave trains are from different directions, and, if so, assess whether the acceleration from DIFFERENT DIRECTIONS imparted on your vessel is acceptable (you’re pushed in 1 direction by 1 wave, then immediately pushed in another direction by a wave from the other train).

When making decisions, bear in mind the direction you’re traveling, and how your motion influences the apparent interval of seas (if you’re traveling into the seas, you’ll shorten their apparent interval / if traveling with seas, you’ll lengthen their apparent interval (and thus lessen acceleration)).
–
Chris Parker

Weather Forecasting & Vessel Routing
Weather & Communications – Hardware, Software, Sales, Consulting, Books,
Seminars

www.mwxc.com
Marine Weather & Communications LLC (and dba Marine Weather Center)
5130 Medulla Rd
Lakeland FL 33811
ph 863-248-2702
fax 863-248-4666

I try to choose my words carefully. I am as specific as I can be. If I speak about something in general terms, or impacting a general area, it means I don’t have sufficient information to make a more-specific guess, and/or it applies throughout the area.

Forecast is in several parts:

1.) Recent observational data.

2.) Analysis of current satellite / RADAR imagery.

3.) Synopsis is weather features, sometimes with a general discussion of predicted conditions in some areas of the region. Synopsis is generally day-by-day for 5-7 days, but I’ll break it up differently as necessary.

4.) Outlook for 5-10 days, or as far into the future as I can make a guess.

5.) Specific forecasts for Precipitation (and squalls) / Winds / Seas. This is normally divided by weather-parameter (Precipitation first, then Wind, then Seas). One reason – if the forecast is wrong, you may see conditions similar to adjacent areas…so it’s useful for
you to be aware of the forecast for adjacent areas. Occasionally, I’ll break this section down by LOCATION, with each parameter (Precip, Wind, Seas) discussed by location.

PRECIP – I usually discuss coverage (in order of increasing coverage: isolated / scattered / numerous or widespread). I also discuss character of precip (convergence can be nasty, but not severe, while convective has potential to be severe), and try to offer a guess as to wind anomalies in the precip – sometimes as wind speed “added to gradient wind”,
sometimes as total wind in squalls.

WIND – speed & direction, as follows: Direction: I usually give this in degrees TRUE. The forecast is NOT so accurate that you should really expect wind of 070-degrees to be from
070-degrees. My main reason for specifying 070-degrees is to offer you insight into the TREND in wind direction. 070-degrees is just about ENE. 060-degrees is ENE. A change from 070 to 060 suggests a BACKING TREND to the wind direction, rather than a forecast for those numbers specifically.

Speed: in kts. I usually only give a specific number, such as 18k. You should mentally “bracket” this – I’m not predicting a steady 18k – you should read this as 18k greater variance…in the case of 18k, you should interpret this as a forecast for 15-21k. If I say “gusty”, add another 20% for gusts, which would make the forecast for 18k & gusty = 15-25k.

Two reasons I give specific wind velocity, rather than brackets: 16k & 18k are both “15-20k”. 18k today & 16k tomorrow suggests a TREND of decreasing wind. TRENDS are very important in your decision-making. Also, it saves several characters – many clients receive forecasts on slow email connections, and every character we can shave off we do.

You may notice the < sign occasionally. It describes a trend. For instance 090@12<15 means 090-degree wind building from 12k to 15k during the applicable period.

Sometimes, I give wind direction in “cardinal” units (N or NW or SSE, etc.), or wind speed in brackets – I do this when I’m so uncertain that I can’t get more specific.

REMEMBER TO CONSIDER WIND IN SQUALLS! My “wind” forecast is generally for wind in the absence of significant squalls. ALWAYS refer to the “PRECIP” forecast for wind in squalls!

SEAS – I give height, periodicity, and direction. Sometimes I specify wind-chop versus swell. Sometimes I give both. If I give both, you should neither add the two nor just look at the largest sea. The real answer is inbetween – generally take the larger sea & add half of the smaller sea to get the total height. Each vessel responds to different seas in a different manner. If you know what’s out there, you can make an educated guess about how your vessel will respond.

6.) CROSSING – forecast between Florida & Bahamas, along N ROUTE (GreatSaleCay / MemoryRock / MantanillaShoal / WestEnd…to PalmBeach /LakeWorth / FtPierce), and S ROUTE (GreatBahamaBank / Bimini /SouthRidingRock…to FtLauderdale / Miami / KeyLargo).

7.) OTHER AREAS – this section varies by season:

• KyW (Key West, in winter only)
• CFL (Central Florida E Coast – CapeCanaveral area, year-round)
• NFL-GA (North Florida-Georgia, year-round)
• SC (South Carolina, not in winter)
• NC (North Carolina – only portion of Coast from CpLookout to SouthCarolina border, not in winter)
• Hatteras-to-Chesapeake (N-bound from CpLookout to ChesapeakeBayEntrance, Spring-Summer)
• Chesapeake-to-Hatteras (similar but in reverse, only in Fall)
• Chesapeake-to-S NewEngland (Chesapeake to BlockIsland/Newport, Late Spring-Summer)
• S NewEngland-to-Chesapeake (similar but in reverse, only in late Summer-Fall)

GEOGRAPHY:
In discussions, I try to divide forecasts into the NW Bahamas (Abaco / N of Nassau / Berrys / N Andros / N Eluthera / GrandBahama / Bimini)…the C Bahamas (Exumas / S Andros / S Eluthera / CatIsland / LongIsland / Jumentos / Conception / SanSalvador)…and SE Bahamas (Crooked / Acklins, and all Islands S&E through the Turks & Caicos).

When giving the specific forecast, I try to zero in on popular Cruising grounds, typically Abaco (a reasonable proxy for the NW Bahamas); Exumas (a reasonable proxy for C Bahamas); SE Bahamas (a reasonable proxy for SE Bahamas and T&C). If conditions vary significantly within these areas, I’ll get more specific. I often have to break the C Bahamas into N Exumas (a reasonable proxy for Nassau / N Andros / Eluthera / Exumas to StanielCay) and S Exumas (a reasonable proxy for Exumas from StanielCay S-ward / CatIsland / LongIsland / Jumentos / Conception / SanSalvador / RumCay).

Occasionally I’ll reference other areas:
NE Part of C Bahamas = the Islands from Eluthera thru Cat-Conception-SanSalvador-Rum, and possibly LongIsland’s E Coast.

Extreme SE Bahamas = Turks and Caicos and GreatInaugua S-and-E.

N Part of SE Bahamas = Samana, Mayaguana, and possibly N parts of Crooked-Acklins and T&C.

SW Bahamas = Andros-CaySlBank

FLStraits = waters S of FLKeys toward Cuba

N Bahamas = Abaco-GrandBahama

If this does not answer all your questions about the forecasts, please
let me know…cheers…Chris.

SUBJECT: Wx Update, Interim Tropical, Wed24, 6aSENT: 24-Oct-12 10:36
MESSAGE:TS Sandy, 5a: 16.3N/77.0W, moving 010T@12k, 60g75k, 986mb.
Deep convection (cloud tops -90C/60,000′) wrapped around Sandy’s center this morning, and, based on RECON and BUOY data, NOAA raised intensity to 60k sustained. RECON found pressure 986mb 5 hours ago, so pressure may be lower now.
Sandy remains asymmetrical however, with a healthy band of strong convection extending ENE from her center toward S Coast of Haiti…then sweeping S&W thru waters off Colombia…and 11N-13N from 78W-82W (well-off Panama). P-S-A lies in an area of weaker, scattered convective squalls at the W edge of this band.What’s lacking is any similar curving “feeder” band extending W-then-N<ENE…though we see some showers & mild squalls E half of Cuba and most of Bahamas & W Atlantic waters N&E of Bahamas…there’s no deep convection, and this activity has the appearance we’d expect from enhanced FrontalTROF activity (there is a remnant FrontalTROF over C Bahamas).Sandy is also dealing with very strong “parasitic” convection just N&W of Aruba and from CaboDeLaVela…to 17N/70W.
Let’s break forecast into 2 parts…short-term & long-term:
SHORT-TERM TRACK…models remain in reasonable agreement thru Fri26 morning, with no further change from yesterday afternoon’s Bahamas forecast, where I predicted Sandy was likely to move close to due-N, very close to 77W…this morning’s forecast is Jamaica (76.7W this afternoon) / Cuba (76.5W tonight) / just W of Ragged-Jumentos (76.4W tomorrow morning) / W of GreatExuma-G’twn (76.4W tomorrow afternoon) / near C & N Exumas (should pass thru some part of C-N Exumas (76.6W late tomorrow afternoon) / close to SpanishWellsEluthera (76.7Wtomorrow night) / just E of Abaco (27N/77W) Fri26 morning.
NOTE that a further NW jog is possible tomorrow night-Fri26, causing Sandy to track just W of Exumas / near Nassau-NewProvidence / over some part of Abacos.
SHORT-TERM INTENSITY…Environment supports further strengthening until landfall in Jamaica this afternoon…expect 70-80k (Cat1) sustained wind this afternoon…interaction with Jamaica should be brief…little intensity change thru Cuba landfall. Sandy weakens over Cuba, probably to about 50-65k sustained wind (borderline strong TS/Cat1).
As Sandy exits Cuba, she’ll enter an area of strong 25k<40k wind-shear. It is almost certain the wind-shear will prevent Sandy from generating stronger winds…so the Bahamas can expect sustained winds 50-70k, gusting 60-85k (more specifics in Bahamas forecast).
During Fri26-Sun28, persistent wind-shear should erode Sandy’s Tropical characteristics – she’ll lose her warm-core Tropical “heat pump” and her winds will become more-uniform throughout her sphere of influence…further discussion belongs in the Long-Term discussion below…but this structural transformation is important for Bahamas & FL, as it explains why strong winds persist for 1-2 days after Sandy departs.
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LONG-TERM TRACK:Although models still diverge beginning Fri26 morning (with some models turning Sandy NNE<NE<ENE toward Bermuda)…some models (EURO & NOGAPS) continue to lie well-W of the other models…and the trend in most of our best models (including GFS) is gradual capitulation toward the EURO solution (which has remained remarkably consistent for a couple days).
Let’s contrast where the different models have Sandy crossing 30N late Sat27: EURO 76W, 965mb / 00zGFS & TVCN 74W, 967mb.
Late Sun28, models differ more: EURO 34N/73W, 950mb / 00zGFS & TVCN 32N/70W, 960mb.
Late Mon29: EURO 39N/73W, 950mb / 00zGFS 33N/66W, 960mb.
Late Tue30: EURO over NewJersey 980mb / 00zGFS 35N/59W, 960mb.
Late Wed31: EURO upstate NY, 995mb / 00zGFS moving NW with landfall NovaScotia Wed31 night, 955mb.
The most-INPORTANT change today may be to the GFS-Ensemble forecast. GFS is our most-reliable model. The GFS forecast most of us use is the most-likely scenario. Computer models take the initial state of the atmosphere, then crunch numbers (based on complicated equations which represent the fluid atmosphere)…to arrive at a forecast. While the “Operational GFS” we all use is the most-likely scenario (based on what we believe the initial state of the atmosphere is)…NOAA also runs 20+ other GFS models – these use the same equations, but start with slightly-different initial assumptions of the present atmosphere.
Previous to today, of the 20+ GFS-ensemble members, only 3-5 executed a N<W turn during the week of Mon29, with landfall of a LO in Newfoundland-NovaScotia-NewEngland dissipated the LO in North-Central Atlantic).
The remarkable change today is all but 3-5 members now execute the N<W turn, with the most-likely landfall (based on 06z GFS-Ensemble forecast) from NovaScotia W of 65W to ChesapeakeBay. Consensus of GFS-ensemble members is along S NewEngland, from LongIslandNY to CpCod.
Timing of final landfall could be Tue30 (EURO) or about Wed31 (GFS).
INTENSITY:Sandy will shift (during tomorrow-Sun28) from a Tropical LO to a non-Tropical LO…but her central pressure is expected to continue falling thru Tue30!
Fri26 onward, the precise track of Sandy’s remnant LO is not critical, because her strongest winds will NOT be near her center! Her winds will be almost uniformly-strong over a distance of maybe 250 miles from her center (a 500-mi-wide-swath)…of winds 50-80k sustained.
MY FORECAST:The ENTIRE US E Coast, from the upper-FLKeys to Maine & NovaScotia should see sustained TropicalStorm/GALE winds of 35k+ at some point tomorrow-Wed31 – some areas could approach 65k sustained. The only areas NOT likely to see wind of 50k+ are: Miami-FLKeys and NFL-GA-SC (these areas should be only in 35-50k range).
I now think there’s an 80% chance Sandy (or her remnant LO) makes landfall somewhere along US E Coast or NovaScotia – almost certainly somewhere N of Hatteras. There’s a 50% chance Sandy could pass within 200mi of Bermuda Mon29, before turning N<W.
At 8am, RECON found pressure 981mb. Based on that, I’m certain NOAA’s 11am forecast will declare Sandy a Cat1 Hurricane.

On December 8, 2012 (at 11:15am) I’ll present a Weather Seminar at the Annual SSCA GAM in MelbourneFL.

I look forward to seeing you there! For more information on SSCA or to register for the GAM (with lots of great speakers and a really fun event for Cruisers!), visit:

www.bit.ly/SaGBdv

s/y Gusto weathered Irene at Treasure Cay Abaco. Read about their preparations & experience with Irene below:

Gusto at double slip at Treasure Cay Marina (Abaco)—evacuated Wednesday afternoon to small condo near our pier.

Prep included–all lines doubled with fire hose chafing around each line (16 lines in all—to pilings)/ all canvas removed/ halyards to top of mast/wind instruments removed from top of mast/any lines loose wrapped around mast/ halyard shackle wrapped with duck (gorilla) tape/55# Bruce anchor w/150′chain and 100′heavy line deployed from stern/canvas hatch covers off/ solar panels off/ everything off deck/ gorilla tape around solar vent intakes/dorade vents removed-replaced with caps/gorilla tape around deck hatches/ heavy dog down opening ports and put plastic over chart table and under ports and over mattress/staysail boom and mast boom lowered lowered, chafing gear applied, and then tied to deck/turned off all power except 12 volt Engel refrigerator–which worked because our AirBreeze wind generator kept us charged and worked wonderfully.  Probably other things I forgot—took two days to do this—–and we’re exhausted!

Took to condo many flashlights- vhf-barometer. Could not find sony allchannel radio we’d bought from you at SSCA—had no communication and really missed a radio.

Wind reported Thursday 120kts. sustained/135 kts. gusts. 90 minute eye.  Only damage port bow guide chock for dock line leading to cleat-was torn off, but double line on cleat ok. 13′whaler dinghy full of water (leaves blocked drains)-bailed with trash cans during eye, lest Merc engine get under water—but ok too. Spot [Globalstar's messaging device] was wonderful for letting family know we were ok. Had no communication other than that.

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And this video from Brett Anderson, s/y Liberty, Colonial Beach, VA

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Image below is from NOAA’s Hurricane Research Division, and approximates averaged winds at 6:30p EDT on Friday, August 26. Local winds may exceed these values by 10-30k.

Irene pummeled Elizabeth Harbor in Georgetown Exuma overnight, with wind backing from NE-N-NW-W at speeds up-to-100k (at-least in gusts), with sustained wind generally in 60-80k range. Images courtesy of s/y Glenice in G’twn.

At BOTTOM of post is estimate of averaged sustained wind in N & C Bahamas this morning…NOTE that sustained wind in any given location may run 10-30k higher than the large-scale averaged winds depicted.

Wind analysis for Central & N Bahamas at 9:30am Thursday, Aug 25, 2011