MONDAY: 03-AUG-15
(Next Regular WX Update WEDNESDAY – AUG 5
NOTE: You can follow me on TWITTER @WX_INTEL
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✭ NEW WIND SHEAR AND ‘DUST’ IMAGERY PRODUCTS ✭
TROPICAL ATLANTIC: QUIET – BUT STRONGER SYSTEMS OVER AFRICA
The Tropics remain quite uneventful, with only a couple minor Tropical Waves across the basin. Dry and stable air – with above normal wind shear in SOME areas - continues to keep a cap on any significant development.
That said – convection associated with the ITCZ has increased, with the ITCZ itself having shifted northward over Africa. In addition, westbound disturbances embedded in the easterly trades are significantly stronger, with these systems coming off the African coast every 2-3 days. And while the global models occasionally (like this AM) try to spin-up a cyclone (albeit weak ones) during the Week 2 period – it’s far too soon to rely on these model projections – especially since these waves are still ‘entangled’ with the ITCZ and typically do not develop into cyclones unless they can extradite themselves from it.
The remnants of INVEST 94L are still detectible over the central ATL, but has zero chance of developing. NHC has begun a new INVEST (95L) for a disturbance near the Florida Panhandle. As mentioned over a week ago – during the warm season, old cold frontal boundaries (and related vorticity centers) that manage to make it to the GOM region will occasionally evolve into a tropical cyclone - and this is exactly the type of 'setup' we have now. However, it appears highly unlikely that the current system near the Big Bend area of Florida will be one of those systems.
TROPICAL STORM GUILLERMO HEADING FOR HAWAII
Former Hurricane GUILLERMO has continued to weaken over the past couple days, but remains on track to skirt the Hawaiian Islands on WED/THU, though it’s likely to be a VERY weak system – quite possibly only of Depression strength. The system is currently ~600NM E/SE of Hilo (on the Big Island), moving WNW at ~10Kts. Officially, the storm is estimated to currently have max winds of 60Kts, but based on RECON data along with Satellite based analysis – MAX winds are more likely near 50Kts, or less.
PATTERN EVOLUTION CONTINUES
All global models remain in excellent agreement on the pattern evolution that will lead to a mean TROF position in the eastern US and a ridge centered over the inter-mountain west. As each short wave moves from Canada east/southeast towards the primary/mean TROF in the east, the western ridge will have a tendency to oscillate to/from the interior west to Plains and then back towards the west. For much of the next 2 weeks, Temps will average 1˚ to 2˚ below normal from the Midwest and Ohio Valley on into interior New England, while above to much above normal readings will persist across the rest of the nation.
Fire Danger levels over the west – already at very high levels – could easily be exasperated during Week 2 as Temps soar in many areas – including areas near the CA coast.
EL NINO / MJO
The latest SST anomaly reading in the benchmark Niño 3.4 region is near +1.7˚C, with low level westerly wind anomalies persisting across much of the equatorial central Pacific (CPAC). However, surface winds in the EPAC are now near normal. In addition, the MJO remains weak and incoherent (though there are some indications that a new cycle may begin somewhere over the western Pacific during the next week or so). For these reasons, very little change in SSTA’s is expected during the next 10-14 days.
ALASKA – MILD BUT WET PATTERN WILL TURN COOLER IN 8-12 DAYS
With high pressure at the surface and aloft developing over the state – a period of downright warm weather is expected in many of the higher population centers from Anchorage northward to Fairbanks – with some record highs possible as well. But by the weekend, and especially next week – stronger disturbances are expected to begin impacting the state from west-to-east – with the warm Temp anomalies easing down; with some below normal readings starting to show up in the western and northern regions as storminess returns.
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CLICK IMAGE to open full size image in a new windowFig 1: Color Enhanced IR (infrared) image of the Tropical Atlantic The remnant disturbance that was INVEST 94L is located at the base of a weak TW in the central ATL, and is westbound at 20Kts, while a new INVEST (95L) has begun for a small disturbance near the Big Bend area of Florida Panhandle where deep convection is located. This system is still part of a decaying cold frontal boundary which should dissipate during the next day or so before the next, stronger cold front now moving across the OH Valley moves into the SE US. The chances that INVEST 95L will develop into a tropical cyclone is close to NIL, however. In the eastern ATL, and especially over Africa, more active convection associated with the ITCZ and westbound waves embedded within it, has continued to increase and shift further towards the north - a seasonally typical development by this point in the season. The latest GFS run has picked up on the stronger wave still inland over Africa, and is forecasting some minor development as it heads towards the central ATL later this week on into Week 2. However, at this time, it doesn’t appear this system has a major chance of becoming a storm during the next 7 days due to fairly stable air that it will eventually encounter, along with marginal shear conditions and cooler SST’s along the (GFS) projected track.
Fig 2: Specialized ‘Dust’ focused imagery from the EUMETSAT product suite. The magenta/pinkish colors correspond to specific light wavelengths that have been shown to correlate with atmospheric dust.If you've been following my blogs this summer, you know by now there are quite a few different products that aim to highlight Dust and other aerosols associated with the SAL (Saharan Air Layer). Many of these products tend to ‘overdo’ dust concentration - for example, the Univ. Of Wisconsin CIMMSS product which tends to rely on moisture content analysis in the lower portion of the atmosphere. The above 24 hour loop tends to underplay actual dust content; but, the 3 different products I've posted this season, when used together, usually results in a fairly accurate analysis. While I haven’t posted any this season, even ‘normal’ Visible imagery taken early in the day, along with MODIS True Color imagery can do an excellent job of highlighting aerosol content. What makes the ABOVE imagery so useful is the simultaneous depiction of deep convection over Africa at hourly intervals, enabling us to get a good handle on Tropical Waves moving across the African continent.
>Fig 3: GFS based deep layered (850mb-200mb) Shear Analysis and 16 Day forecast for the Atlantic. Another new product for my blog – highlights shears above 25Kts. I’ve chosen the 25Kt ‘threshold’ since shears of this or higher magnitude are usually too strong to allow cyclone formation. OTH – once a storm forms and intensifies, strong shears will actually appear well removed from the storm center as its outflow intensifies. At this time, note the persistent high shear over the CARIB which is primarily being induced by the strong El Niño event in the Pacific.
>Fig 4: Satellite analysis using combined IR and WV (Infra-Red / Water Vapor) imagery, overlaid with the wind shear analysis. Convection is now weaker and far less concentric / symmetric around the center of GUILLERMO, with most of the deep moisture and isolated moderate-strong convection in the northern semi-circle. Wind shears have continued to steadily increase, and is now out of the west at 20-30Kts across the bulk of the storm. The latest official forecast track keeps the storm parallel to but north of the Island chain.
>Fig 5: OHC (Ocean Heat Content) and SST analysis. SST’s (right panel) near the storm are now around 27˚C, a value typically associated with the threshold for maintaining a tropical storm. However, the total heat content (left) is marginal at best – and as the storm tracks futher to the north during the next 48 hrs, SST’s (and OHC) are likely to be too low to even maintain tropical storm intensity; and it would not be surprising to see the system downgraded to a Depression by the time it nears the Islands.
Fig 6: 16 month loop from the JASON satellite that measures Sea Surface HEIGHTS (SSH) (and anomalies). The warmer colors (‘Reddish to White’) correspond to above normal SSH’s with cooler, bluish colors corresponding to below normal ocean surface heights. Because water density increases with cooler Temps and lowers the warmer the water is – the above imagery serves as a great proxy for total ocean heat content. After faltering last summer, El Niño began to intensify rapidly this spring, with a very large area of well above normal SST’s and (and very warm sub-surface Temps) are now affecting much of the eastern Pacific.
Fig 7: GFS Jetstream Forecast for next 2 Weeks. At the beginning of the forecast period, we find the sub-tropical centered over Texas with a TROF extending from Hudson Bay towards the Mid-Atlantic region. Heights are rising over Alaska as the downstream TROF near the PAC NW gradually weakens and give way to rising heights. In about a week, the sub-tropical ridge will generally extend from the southwest US towards the SE US, with the jet stream remaining well to the north of the ridge. While it won’t have any meaningful impact on weather conditions at the ground – the sub-tropical jet appears to strengthen at times between the Hawaiian Islands and the CA coast – primarily induced by El Nino. As we head into Winter – this sub-tropical jet holds the promise for a stormy winter in the west.
Fig 8: Temperature ANOMALY forecast for Week 1 is based STRICTLY on the MOS data forecasts from the todays 12Z operational GFS model run with minor adjustments towards the raw model data points. Above normal readings across much of the nation as cooler Temps are felt from the northern Plains to upper Midwest and interior Northeast. Confidence in the forecast anomaly Pattern and magnitude is solidly above average now, with readings of ‘5’ and ‘4’ on a Scale from 1 to 5 for the anomaly pattern and magnitude respectively.
Fig 9: Running Precipitation totals for US during Week 1 (and only for totals > 0.75”) based STRICTLY on the GFS Heaviest Precip will again be over the far southeast US, with a ‘band’ of heavier Precip as a series of cold fronts trigger T-storm activity from the Midwest and OH Valley - eastward to the Mid-Atlantic states. A relatively dry period is expected across Alaska (though pop-up T-storms are expected in parts of the interior (with increased wild fire danger.)
Fig 10: The Week 2 Temperature ANOMALY forecast is based on the 12Z run of the GFS (70%) integrated with the 12Z GFS Ensemble (20%) and the ECMWF ensemble (10%) using the projected pattern along with explicit surface and 850mb (~5,000 FT) Temp forecasts. Some Temps are adjusted for known / expected anomalous thermal patterns & projected storm system passages.A very warm period across the western half of the nation and the deep south – but ‘cooler’ conditions should persist in the Midwest and Ohio Valley. Confidence in the forecast anomaly Pattern and magnitude is close to average by summer standards – with reading of ‘3’ on the overall anomaly pattern, but is still a ‘2’ for the magnitude on a Scale from 1 to 5 due to run-to-run variations in the exact location of the western ridge which will determine how far to the east the heat can reach.
Fig 11: Today’s Temperature anomaly forecast is based STRICTLY on the 12Z run of the Operational GFS using the GFS MOS forecast data A very warm period ahead – especially in the ANC-FAI region with abundant sunshine. While anomalies are likely to remain on the positive side of normal during Week 2 – there will be a decided increase in cloudiness and Precip across much of the state.
✭ The Next REGULAR Weather Update will be on WEDNESDAY, AUGUST 5 ✭
‘Normal’ Summer Update Schedule is MON, WED & FRI - but can vary at times.
However, whenever Tropical Cyclones Potentially threaten the US, I’ll be providing Updates 1 or more times per day
Steve
NOTES:
1. A GENERAL Glossary of Weather Terms can be found HERE
2. Another Glossary of weather terms is available HERE
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