HS 100

marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 900 am EDT Sat 18 may 2013

.Forecast discussion: major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.

06z GFS/NAM were mostly consistent with their respective previous runs over the W Atlc for the next few days. GFS 10m winds look reasonable and are supported by 00z ECMWF/UKMET. 06z NAM overdone with SW winds offshore over nrn mid Atlc waters sun ngt and Mon...up to 30 to 35 kt balt cnyn to Hague line zone. 00z ECMWF/ UKMET are slightly slower than GFS in dropping cold front S off new engl coast late Mon into Tue. These mdls then all move weak sfc lows E alng front thru srn new engl waters Wed. Overall will not be making major changes from previous nt1/nt2 forecasts in this mornings updates. 06z multigrid wavewatch sig WV hgts fit well with latest W Atlc ship/buoy obs. In the Med range Tue/Wed will blend 06z mww3 with ECMWF wave mdl to account for some minor sig WV hgt differences.

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A cold front extended from E to W across the nt2 waters near 34n. A high pres center was N of the front over nrn nt2 and a high pres ridge was S of the front over srn nt2. Winds across the area were E to NE 10 to 20 kt from the front N to 40n...S to SW 5 to 15 kt S of the front to 31n and variable 5 to 10 kt N of 40n. The 06z seas state analysis indicated 2 to 7 ft with the highest E of 68w.

Short term...the cold front will stall just S of Cape Hatteras overnight...then remain through tonight before lifting NE across the area as a warm front sun and Sun night. The high pres center N of the front will drift slowly E late tonight through Sun night.

The models are in good agreement with the short term pattern. The NAM and Gem are higher with winds over the nrn waters by Sun night. Both have small areas of 35 kt. This looks overdone with the cold waters and the waa. Prefer the weaker solution with winds in the sly flow 15 to 25 kt.

Long term...the nrn part of the high pres ridge weakens and move to the se Mon. A 3pt low develops on a front N of the nrn waters Mon. The low moves well E of the area pulling a cold front S into the nt1 waters Tue. The front stalls near 40n later Tue. Several weak low pres centers develop and move E along the front Tue. Then the front lifts back N as a warm front Wed.

The models split on the long term pattern. The GFS/ecwmf and UKMET stall the front Tue and lift it back N Wed. The 00z Gem takes the front move S of 40n Tue and stalls it Wed. All the models keep winds to 25 kt or less S of the front with the strongest winds S of any low pres centers passing along the front. Plan to use the front as the boundary and not try to time any low pres centers crossing the area.

Seas...00z multigrid ww3 and the 12z ecwmf wam have initialized well over the cstl/ofshr wtrs...the models are within one foot of the buoy obs. Plan to use the multigrid ww3 mdl for the ofshr fcsts. For the highest seas on Mon the models are within one ft of each other. The 00z ecwmf was not available yet.

Extratropical storm surge model...N/A.

.Warnings/forecast confidence...Preliminary. Any changes will be coordinated through AWIPS 12 planet chat or by telephone:

.Nt1 New England waters... .Gulf of Maine...none. .Georges Bank...None. .South of New England...None.

.Nt2 mid Atlc waters... .Hudson Canyon to Baltimore Canyon...none. .Baltimore Canyon to Hague line...None. .Baltimore Canyon to Hatteras Canyon...None. .Hatteras Canyon to Cape Fear...None. .Cape Fear to 31n...None. $$

.Forecaster Clark/oszajca. Ocean prediction center.